They will not file for bankruptcy. They are way too big–I mean, 49% of it is still owned by GM. They will downsize and prune away, but still have a lot of capital to play with. If all you are worried about it is GMAC going out of business, then you are completely safe.
Also, GMAC mortgage is the prime unit, and while ResCap is integreting all their businesses, they still separate their prime paper from the subprime when it comes to loss serverity.