I think Manmohan Singh can rule for another 5 years. He is the best bet India has.
Rahul Gandhi is not even a minister, so progression says he will take another 5 years for training, may be as some cabinet minister. Other than that he will stick to his party role. He did not exactly shine as a General Secretary. Among all the nepotism and a** licking that Congress has, the party still hosts the biggest repository of intellectuals(Granted there are intelligent idiots like Kapil Sibal) among all parties. Since Sonia had successfully turned it into a mafia, there is a balance between popular mass leaders and educated people in the party. The popular mass leaders are typically given state leadership positions(like the late YSR), a*s lickers are usually given ceremonial posts. But the highest levels of power seem to be well guarded from the crazyness. At least until now, it is guarded from the political blackmail of the allies. So Lalu got his little fiefdom called Railways where apparently his crazyness led to the revival of the largest employer of India(I am pretty sure Lalu's biggest achievement was letting his babus implement their ideas without the egoistic c*ck-blocking typical of politicos). DMK had its fiefdom called Telecom for a while.
My point is sensible people have been occupying important positions in government so far, and there is no other party or coalition where I can expect similar stability.