At this point what exactly happens in Egypt is anyone's guess. Still, I think over the past few days some constraints on the actions of various parties has emerged that limits the possible outcomes. I'll review over what I think I see in current events, with the caveat that not knowing specifics about Egyptian institutions or the personalities of the key actors involved no real predictions can be made.
As I've written before, the military seems to be the central institution concerned in the current struggle. This NY times article goes into a decent overview of the situation with the military, I'm betting the regime is regretting not paying them better now. The major constraint is the questionable reliability of the armed forces, while the armed forces seem to be basically loyal to the regime there seems to be significant enough doubts about the rank and file that leadership has been reluctant to test this. While they may have been able to use the army to suppress the protests initially, that particular ship has sailed and I doubt they will test this at this point.
Which brings up the second constraint, the amount of support the regime gets from the United States. While this influence shouldn't be exaggerated it doesn't seem unlikely that the amount of aid received from the US and the risk of alienating its US backers may have contributed to what I think may have been a critical delay in the use of force. While the counterfactual is unknowable, attempts to break the protesters would likely have been more successful in the first few days, either by pro-Mubarak mobs or by a military whose rank and file may have been more reliable in early days but has reliability has since become more questionable.
The third constraint is the late use of force to try to rout the protesters and the following international reaction. From what I can tell, this action was basically a high reward but high risk though low severity gamble, though it is not surprising the regime took it. There was a chance that the protesters would break, but this was small by the time mobs were actually put into play. However, this alienated foreign backers of the regime, which threatens the aid the military received. This was a bad call on Mubarak's part because now there is something of a rift between the two which was less pronounced before. The military kept its distance from the counter-demonstrations and probably has little to worry about in the medium to long term with its funding. However, Mubarak's actions gave an incentive for foreign regimes to distance themselves from him, both to help relations with other powers and whatever regime ultimately has power in Egypt. This makes Mubarak something of a liability to the military, though continued allegiance to him may have other benefits. It certainly made keeping those benefits potentially more costly in the short term, however.
The next constraint is the lack of clear leadership or even clear factions within the protesters. This has two effects, it makes them harder to bargain with and it makes it harder to try to divide and conquer. There remain fears about the Muslim Brotherhood (legitimate or not, I have mixed feelings on them), and perhaps more generally, what effects any perception of them winning will have on the rest of the region, no matter their long term role in Egypt. My guess is that this will make the situation drag on for longer than it otherwise would have, beyond that I think it will make it more unlikely for the government to offer strong concessions. The army simply won't feel any confidence that they can influence what follows strongly enough without knowing that there is a leadership in place that will be able to deliver on any agreements made.
The next constraint is closely related, and that is that always volatile nature of the Mid-East and fears of jihadist groups using the situation to their advantage. While I think this is unlikely, I do think that fears of this will secure the current Egyptian regime, and in particular it's army, basic levels of foreign political support and if necessary funding, to be able to hold on as long as they need to. I don't see foreigners sticking their necks out simply to ingratiate themselves with any new regime, risks elsewhere in the region will make this outcome unlikely.
The last constraint is the seeming lack of serious unrest in the rest of the country. As long as the army doesn't break ranks it seems unlikely the protesters can break the regime from their current outpost. Serious unrest elsewhere in the country could possibly threaten the regime's stability and cripple their revenues which would stand a good chance of unseating them. Lacking this, it seems reasonable that they could keep the protesters bottled up for some time without being forced to give in.
So to some this up the outcome will depend largely on the deliberations at the top ranks of the military. I think they are likely coming to see Mubarak as something of a liability, as a face saving measure they will probably provide some sort of temporary position but I think they will sacrifice him once the situation begins to seem too costly. I believe their ideal outcome will be for Suleiman to step directly into Mubarak's position in some form of negotiated process, but without knowing more about the Egyptian military I will confess that there are likely many political outcomes possible within staff negotiations that I am unaware of.
From the standpoint of the protesters, I don't see them having the leverage to get too many concessions. However, they may get increasingly desperate, fears of arrests and repressions after they leave the square may force them to remain there until some kind of settlement is reached. I have no idea if they will accept Suleiman or not, but it is hard for me to see how they can get new elections in the short term. Perhaps what they will need for their security will be something like one of their leaders brought into the regime to insure their safety, I have no idea who could fill this role however.
On the whole, there seems to be an impasse. The military is too uncertain in its loyalties to allow a crackdown, and in any case the military remains sufficiently well liked that it can be assured a strong voice in whatever comes next, whether this is driven by the protesters or the current government makes little difference so they have little incentive to crack down just to insure Mubarak's survival. Their optimal move seems to be to simply sit this out and wait and see what happens, which may mean it will be awhile till this gets resolved. The end result will be short of a bloody crackdown that solidifies the regime and less than a collapse of the regime. Whatever happens, the military will probably come out ahead and play an increased role under the new regime, whether chosen by elections or headed by Suleiman.
Or to put this whole post more succinctly, I think at this point things are at an impasse and will go in favor of whichever side the military throws its weight behind. However, since the military is on good terms with both sides the military really has no incentive to go either way since this will mean alienating someone. This makes the result unpredictable, the longer this goes on the greater chance that something unexpected will throw things into chaos (imagine what a large terrorist attack could do right now), but barring the unexpected, this simply becomes a test of endurance between the two sides.