I am going to retile my bathroom.?

It's probably not regular drywall behind the tiles if they are ceramic. It's going to be cement board or tile backer board. I've seen it done many times on HGTV shows and they always pull it down to the studs. I'm thinking it's too hard to remove the tiles without destroying the backer board. Cement board is not very expensive and only needs to go where you want tile, you can put regular drywall up anywhere else (moisture resistant type, maybe).