I get your point, but I find it pretty significant that Bruce has talked about Maiden being like a family; you don't always have to agree with each other about everything, but they're all part of the one mothership. This rhetoric has been pretty prominent in recent years, perhaps because of Bruce's cancer and all, and that kind of hints towards that they're all in this together or not at all - you can't replace a family member, so to speak, no matter whether you always like him or not.
I might be on the wrong tracks here and I respect different opinions. But, especially in the light of recent years, with every tour, every album and every single concert being kinda "sacred" and definitely not something you take for granted nowadays, I personally can't see them going on, should something terrible happen or just someone being unable to continue.