A tile on the floor of our shower stall has come loose. However, in a few months (not much earlier for logistical reasons) we’re having the whole bathroom redone, including a complete replacement of the shower. What I’d like to do is replace the tile quickly and easily and without really caring if it’s a long-term solution or not, so we can keep using the shower until it’s ripped out and replaced.
If it's going to be for a short period of time I'd get some silicone adhesive and use that to put the tile back in. Don't bother grouting either, just use the same adhesive for that too. Just make sure the area is totally dry before sealing in the tile and let the adhesive cure for the recommended time before using the shower.