even if your live rock is dead it will soon become living again if you add some new live rock dont clean it in fresh water and there shuld be no reason it die in the first place all live rock with have stuff growing on it eventualy..
you shuld look out for rock that is in variuos stages ie has plants in the form of micro algee groming on it things that look like moss..
and red coralline algae on it you might be lucky to get some other things like crabs and small corals and who knows what else .. this is what you want to spawn new rock your self ..