If a rosette never blooms again, it's monocarpic. This definitely addresses the mystery of the blooms being so rare.

It's the speed at which the dying part happens that seems to be debated. In decades of having them, I've not seen a whole rosette die. But the older rosettes usually get trimmed away, gradually, over time, as they get beat-up from moving plants around for a drink, repotting, and going inside/outside, a couple bouts with frost-damaged tips over the years. I think 15 yrs is prob the longest my plants might have kept any particular leaf. But if they never got disturbed, who knows how long an individual leaf could persist? I would suppose that, like many other monocarpic plants, the mama rosette leaves fade away very gradually, over a long time, probably 1 leaf at a time, after establishing many pups. Not at a pace that would be called, "it's dying," or noticed at all by those who aren't interested in such minute details.

I can only speak for S. trifasciata.

To try to investigate this, I was going to mark the rosette that bloomed a couple months ago, but looked just now & the flower stalk is completely gone already. I can't tell which rosette had it. Will be more ready next time.