We've been in our new house for about a month now...a couple of weeks
ago we were removing the old shower doors and eight or so of the
shower tiles came off of the wall (the wall opposite the shower head).

They've been off for two weeks or so. Is this something I need to
replace ASAP? Could it cause mold or damage to the wall etc...?

We definitely want to do the bathroom over but most likely it won't
happen for a couple of years. Should I just go and buy some similarly
colored tiles and put them up in place of the missing tiles? The eight
tiles that came off are all right next to/on top of each other.

This will be our first tiling job, so any advice on replacing those
tiles is appreciated.

Thanks