Desolder the chip that looks blown up.
Use multimeter to measure continuity between gate, drain and source pads of the other mosfets to determine if they're shorted or not
Measure continuity between input and ground of the vrm controller for a basic check to see if controller is shorted / dead.
Measure resistances between mosfet gates and the vrm controller (or the phase doublers), see if there's anything shorted between those..
If you're lucky, the video card used pairs of mosfets, in order to reduce heat on the mosfets, so if just that mosfet is dead, the video card may work and run (at least for testing purposes) with just one mosfet out of the pair, on that vrm phase.
These videos are in russian, but maybe you can follow the tests he makes to see if other parts are faulty :
mosfet dead on one phase of the vrm, took the controller with it :
and a bit unrelated, but cool how he detects the memory chips are shot
The whole channel is worth bookmarking if you're into repairs