It is cheaper for China to engage India via Pakistan. that is s much a truth as US found it cheape to engage USSR via Pakistan. After the party is over, everybody gets up and just leaves. The same will happen in this case too. The only loser will be Pakistan. Looking at the benefits that they can get:
1. It is a deterrent against an Indian attack or war that just does not seem to happen.
2. The Kashmir card is withering away due to the increased extremism bearing fruits within Pakistan itself.
3. Army whose favourite tag line for their political and social dominance in Pakistan used to be Kashmir is actually so stuck up with its prodigal sons that Kashmir does not even seem to be on its mental horizon. Now these Tahrir links are keeping them quite busy.
4. In the course of this strange parity seeking, the economy is down in the drains, so much so that if international bodies do not lend money then Pakistan will truly eat grass "ZA Bhutto, 1973".
5. China gets to sell arms on credit + also continue to maintain the trade imbalance so free ride in the short term.
6. Geo-Strategic position means that Iran is not a friend of Pakistan, the Arab brothers are funding Taliban, Afghanistan which used to be the whipping boy of Pakistani Army is getting back at it, US is losing patience with the aid and the friendly strategic assets being protected and on top, the political circus continues on lines of protecting the extremists or going after them.
Truly Pakistan is the only selfless state in the world. It likes to damage itself endlessly in the course of various friendships that it chooses. It is never a Vassal state though.