Renovate it immediately (estimated $60 million in 2010 dollars)
Do not close it while work is done. Work around students and staff.
Patch it up, then move students and staff back in next year so it's usable until a new school is built.
Do not move back in. Construct a new school immediately.
Its life as a school is over but it's a beautiful building. Sell it to the private sector for $1 with renovation required as part of the contract.
Its life as a school is over. Sell it to the highest bidder to do with as they please and use the proceeds to help build a new school.