Why would you want the regime to fall if there is nothing to replace it? If Mubarek simply packed up and left, the likely result would be one of two possibilities: A military junta-style regime, or a regime created by the most organized of the protestors - the Muslim Brotherhood, most likely. Either result would be bad, and the struggle to fill the power vacuum could easily lead to intensified violence.
What we in the west should really be hoping for is a ‘soft landing’. Elections were scheduled for September. Mubarak has already announced he won’t run. So either let them go on schedule, or accelerate them to May or June or something to give people a chance to raise support but make it close enough to clarify that the regime is really going.
It seems to me that the best result would be for Mubarak to announce that he is forming a short ‘caretaker’ government to keep things running until a new government can take power after the election. Announce that all current top leaders have tendered their resignations so it will be a truly new government and not just business as usual. Enlist the army’s support, and rely on them to keep order and make sure the election is fair. Invite international election observers to show that the election is fair.
If the people still riot and won’t stand for that, then the next step would be to call together some sort of hearing, bringing in representatives of the various protesting groups to bang out some sort of transition plan that would be acceptable to all.
The last thing you want is the government simply vanishing, leaving a power vacuum behind and causing public services to shut down.