The plumbing repairs appear to have been successful. No leaks from either shower. We received word from the rental-management company that they will send a contractor next Monday to (a) replace the toilet in my bathroom with one that should be less susceptible to clogging and (b) repair the hole they cut in the wall yesterday. I passed on Cheryl's suggestion of putting an access hatch there rather than just sealing the hole off, in case they ever have to get back in there again.
Once the repairs are done, we can return the shelves to their regular position and reattach them to the wall, and put stuff back on them.