I got lucky on the last one. We heard it letting go! Still had a mess but it wasn't as bad as it could have been.
Wasn't so lucky on the washer up stairs. The pan had a tiny drain that was easily blocked. The new pan has a custom 2" drain and there's a second one in the room's corner.
So what happens next? This week the fridge's ice maker got stuck filling and water started coming down stairs while I'm ballasting. I never even heard of a fridge doing that! Now I know. If it can happen, it will happen.