Scenario 2, 99.9% won't happen, as I had a slight oversight when doing my plumbing and cemented the stand pipes into the bulkheads.
I left that .1% so I don't sound like a fool in the future when my PVC cement fails me for the first time ever..
That leaves your first scenario, which is possible. But I think if the bulkheads themselves leak, it would be manageable to replace them with the aid of a towel so soak up any leakage while replacing. A possible nuisance for sure, but manageable and easy to keep check of on a daily basis. I shouldn't say this, but I have always had good luck with bulkheads not leaking.
The leak is fairly slow.. over the course of 1.5hrs the level in the overflow raised by 1/8" (in a 8.5"x6" footprint).