First, recheck everything else like video card (often moved in slot when a system is moved if the monitor cable is attached) and other cables, and if the 'sink fell against anything check that again.
You wrote seems to be working fine but locks up. How is that working fine? Monitor the temp when it locks up. Had you ever ran a stress test like Prime95 to check stability prior to this? If not, you won't know how it compares now, but you should do that now anyway and note the temp.
The problem now is that after running instable you may have file corruption on any files written in this period. To be sure you need to run chkdsk and ideally a clean install of windows, or at least a separate testbed install instead of wiping out the present install so you have a better idea if it still locks up.
It is possible in theory that the heat has damaged the CPU, that bonds are intermittent at a certain temp or that the heat spreader has popped off the core in the middle and only held down by pressure now. So yes in theory if nothing else helps it is possible the CPU is damaged. A surer sign would be trying it in another system, or ordering another CPU from a place with a good return policy so you have a 2nd CPU to try.