In my opinion, put him in about 1-2" of water so that his neck wound won't get wet. That's the solution. Res's can slurp water just like a snake. He may even eat a few pellets. You can put him in there for maybe 30 min. 3X a day.

Moreover, get a second opinion. Yet perhaps the vet thinks there's internal injury so the turtle can't drink or eat. I don't know.

Yet it sounds dire and I'd go with giving him a little water.