Re: Ceramic soap dish fell off tub wall
IF the wallboard or other surface behind it is still sound, clean it up (both the wall and the soapdish) and use some thinset mortar to put it back up, then re-grout around it to make it watertight.
Of course, I have the mortar and grout powder, so I can mix some up when I have to; hopefully you can get a small quantity if you need to.
Goop is excellent stuff, but for this application I'd consider it a temporary fix.
Just gluing it back up is only part of the problem. You also need to seal around it to make it watertight. Add in a factor of wanting it to match so it looks ok with the existing shower surround, and you will need to grout it. If you're going to that extent, you might as well do it right and use the thinset mortar. But really, this is not difficult (even I can do it

)