1) to some degree. the algea might be viable but the bacteria and protists are defineatly dead. but the good new is you can start it in with some"fresh" live rock and have it come to life again. dont do this in a cycled tank, it will re-cycle.
2)about a 100 pounds total, in the end. that either means buying 100 lbs of LR, or 50 of LR 50 reg., or 25 LR 75 reg. you just have to wait for the reg rock to become "live".