The last time one of my sims had a bladder failure it was pretty much on me...I forced them to keep doing something else when it was pretty clear it was going to cause a problem. I just didn't want them to waste time going to the bathroom until they finished what they were doing and was hoping they'd still make it (they didn't).
Normally though, I send sims to the bathroom far more often then they need to. As someone who drinks an insane amount of water irl...and thus uses the bathroom pretty much every 2 hours...I tend to have my sims hit up a bathroom every time they walk past one.
I even have the bladder motive modded in my game to decay 20% faster than normal...because I feel like the sims don't need to use the bathroom often enough at default.