Tile – Need to fix tile that has fallen off

To be honest, I'd probably be lazy here, and stick it back on with a thin film of a good commercial adhesive, thinly buttered on the back of the tile. Leave the old adhesive as it is. The old tile will fit perfectly. This is NOT something for superglue, but perhaps for something like liquid nails in a tube. Buy it in your local home center or a decent hardware store.

Use some tape (the handyman's secret weapon is duct tape, so says Red Green) to hold it in place, but any decent adhesive will have enough tack to keep a tile there while it dries.

Really the hardest part to do is to re-grout around the replaced tile. I'd not be at all surprised to find that available in a squeeze tube too. So I checked, and indeed it is, here, for example.

It looks like all that is seperating the drywall from the tile is a bead of caulking. To fix this, I would first remove all of the existing caulking. Then I would cut out the area of the affected drywall and patch in a new piece, using the factory taped edge as the end that butts up against the tile. Tape, mud and sand the new section and paint to match. Once finished, install a new bead of caulking along the entire length and it should look like new!