How to repair a fallenundermount sink
Wow, so sorry for you in your situation. I don't kow what your countertop is made of so , here is a repair for granite, hopefully you can apply replacing with repairing:
This second link is fixing a fallen sink to granite:
Best to you.
Can you see if it had clips or was it only cemented?
Our marble co here will come out to reattach the sink, but have to disconnect the plumbing first. Let set up for 3 days, then hook plumbing back.
Just look under it the clips came off just pick them up and screw them back in there is 4 clips in all one on each corner