It’s still there… 4 full days and made it to closing time. Now that I understand the motivation mechanics a bit better, it makes more sense.
I’d assumed that motivation would keep decaying to 0 even without being attacked, and the Pokemon would eventually get bored and leave, rather than hitting a lower limit and staying. Which I suppose means you could end up with a Pokemon trapped forever in a gym if no one from another team ever visits. Edge case, but easy to imagine.