My sims can't swim.
My Sims can't even swim in the ocean and I own the Island Paradise expansion pack, they also dissapear after they finish time in college, when I go back to their hometown I no longer have a household...
Forum Discussion
4c46cdf0dc440ee9 The missing open water options is a known issue in the 64-bit Mac version:
[CURRENT ISSUE 64-bit] All open water options missing | EA Forums - 11148737
Sims disappearing when they return from University is also relatively common in macOS. If you have a save from when your sims were still in University, and you're willing to use mods, I would suggest adding NRaas ErrorTrap, Overwatch, Register, Traveler, and MasterController. More information about all of them is here:
Sims 3 - Common Game Fixing Mods - Hero Approved | EA Forums - 8291748
I would also suggest running an MC reset before your sims leave for home. Click the admin building's map tag, or an in-game computer, and select NRaas > MC > Town Options > Reset Everything. The reset can take a few minutes to run, depending on your hardware and what's going on in the world; you'll get a notification when it's done. Run this not too long before your sims are scheduled to depart.
Make sure your Mac is plugged in when you try to send the sims home as well. The travel transition is somewhat demanding, and all laptops throttle performance to preserve battery when not plugged in.
If this doesn't help, let me know. There are other, more intensive interventions you can try, or I could try to fix the save for you.
