Alter Bridge is Creed minus Scott Stapp, so those guys have proven through thick and thin that they’re all about it. I’ve seen interviews with Mark and Myles, and those two are very close friends. It would take something massive, I think, for a major change in Alter Bridge to happen, and all of them are level-headed, stable, and at least reasonably sober (meaning no substance *issues*).
Avenged were friends before they were a band. They survived utter devastation and never lost their resolve for their band or each other. It remains to be seen if Brooks is fully enveloped in that family (I hope so), but the remaining four are likely to stay together, again barring something seriously catastrophic. Except Johnny. Fuck that guy. (jk) But seriously, they’ve been through a lot. They’re now stable family men who approach their craft logically and thoughtfully and they are likely to stick it out, as well, until they decide they’re done.
No one can ever say whether a band will retire from old age together or pack it in earlier, but as long as both bands continue to find personal reward (and enjoy the money), there’s not likely to be a significant enough reason to let it go.