so what happens with my acro crab?
 

My SPS die off is still ongoing, wondering what happens to the crab once the last piece of acro bites it.

Will it survive in the rock water?

I don't think their long term prospects are very good out of the colonies. I've had to give away several, had one really pretty blue one once that kinda sucked to have to give away but felt it was better for the animal to go to someone who had colonies still.

They will perish. This has been my experience anyway.