My grandpa is in the hospital for monitoring because of low kidney function because of due from ct contrast. they are monitoring and giving him iv and electrolytes overnight. will this cure him or the damages is done?

Hard to tell without a complete history. Most people who have a reaction to contrast resolve with fluids and rest.

If the issue is contrast induced nephropathy there is a good chance it will respond to iv fluids. Otherwise, the medical team remains your best resource for further clarification.

This renal issue will be clarified as treatment proceeds. Keep close communication with hospital team, and ask questions regarding status. Often, family conferences are very productive.