Well stated, Mosh. It really IS unprecedented. I mean, yes, the Stones are really the only example out there. And as you rightly put, Yes and Priest keep going. Kansas is doing it too. But in all honestly, Maiden is bigger than Kansas, Priest, and Yes. So you look at the Stones and see how you compare.
Loved your point about some of these bigger organizations really being that - a big employer with many on the payroll. There is...likely, an obligation felt to those folks. So if the band can continue and deliver at a level people love, then why not?
I don't really see Maiden continuing without Bruce at this point. Back when he left the first time, it made sense for them to continue. It didn't work out, Bruce returned, and they've pounded it for 20+ years, and aside from Metallica, Maiden is the biggest metal act on the planet. I can't see Steve continuing Maiden without Bruce. Without someone else in the band - yes. Without Bruce and that identity? No. They are just too big now.
Overall, I've seen Maiden many times, and saw the Legacy of the Beast tour twice. Bruce was awesome. But he struggled with high notes. Aces High, and some others. But his performance was just so amazing that it wasn't a big deal. And that's why, at least for me, Bruce gets a pass. He's running all over, singing at a high level, and if he misses some higher points, so what. Whereas some other singers, who don't do anything else but stand there, and you are fixated on their voices...it is much more glaring.
For me though, Maiden would be done in my eyes if Bruce stepped down at this juncture. If any of the other guys stepped down, including Steve, IMO, I think Maiden continues just fine. But Bruce is the ringmaster on stage and the voice of the band. At this stage, without him, there's no Maiden.