I don't question that Aerosmith is hugely popular in the older (twenty somethings) generation. I question where they will be in five years. They haven't put out anything new in a while, and if they did, I don't think it could compare with their older stuff.
When the deal was originally signed with Aerosmith, it must have been recognizable that they were in the twilights of their careers. I would equally question signing the Stones (you never know when Richards is going to keel over). If you expect the attraction to have recognizability for a long time without serious overhaul, I would have suggested signing the Chili Peppers or DMB, both much younger bands with huge fanbases.
Now that the ride has a band branding, I don't think there's any going back. It will either be Aerosmith, or just the RnR featuring no one. Do you guys really think they might replace Aerosmith with another real band once their 'time is over'? I'm curious if WDW would do that, or insert a fictional band. But I guess if they made it a fictional band, no one would recognize the fictional songs in the ride, and it may not be as popular...