We've already talked about the possibility of impeachment of Musharraf by an alliance in parliament by the People's Party and Muslim League-N in Pakistan. At this point, it appears as if Musharraf may try to preempt them and step down himself.
Musharraf has made no overt signs that he is going to resign, but different sources (particularly Stratfor) have been talking a bit about signs they have seen: The Telegraph (UK) has quoted anonymous top aides as saying that the President may be stepping down in a matter of days. Stratfor claims that some of President Bush's senior advisers are investigating the most elegant way for Musharraf to leave.
While Musharraf has seemed to fight tooth-and-nail to hold on to his power in the past, he may have not realized that there is none left for him to hold on to. If the Bush administration is successfully aiding the power transition to a Sharif-led government, Washington's relationship with Pakistan may indeed remain strong, in large part thanks to the political power of the Pakistani Army (a highly pro-Global War on Terror entity).
The US should continue helping Musharraf move out, and both welcome and support the new government, in hopes that US-supported Pakistani anti-terror operations are not hindered. In fact, as we've speculated on earlier, a more widely-supported coalition may reduce political support for the Taliban in the northwest, as they will no longer represent an anti-Musharraf institution, but instead an anti-state one.