It's not that simple. Actually, don't worry about MQM - their support of Musharraf is non-ideological
. Neither do worry about PML (Q) too much - in the end of a story, they are just a splinter of PML, they can find common ground if they really want
Actually, having PML(N), PPP and, say, ANP work together might be a tougher part of the job.
Now, the reason Musharraf isn't likely to be impeached is different: it's not just a matter of the democratic process. Remember: they will always have to live both with the Army and the religious fundamentalists, and both present non-trivial problems. Now, the Army is easier to deal with: at least, there is some notion of the chain of command. Musharraf isn't the head of the Army anymore, but he does have some influence there (let's put it this way). Even if he didn't, somebody would: it's not clear that anyone wants to deal with that somebody. Shakh Nawaz once got burnt already - he'd better be careful this time.
In addition, even if there is now a sort of a truth between the PML (N) and PPP, they have always hated each other. Remove Musharraf, and they go at each others throats. It's not clear that they want it - and it's not clear that anyone wants it. Musharraf still has a role to play (or else, it would have to be played by somebody else).
