Hi, Myke! Welcome to Interference!
Please, don't get scared by some answers, some people get too defensive of their band even when there's nothing to defend them from. I find your question very interesting as it comes from the "outside world".
My opinion is that if any member of U2 leaves it will mean the end of U2 as a band, that's what most fans expect, I think, there have been polls in other big U2 sites about this and even if it were Larry (drums) or Adam (bass) most fans say they think they should not continue U2 in those circumstances, in the case of Bono and Edge (guitar) almost nobody consider it as possible.
Why is it so? you asked in another post and you compared U2 and Guns'n Roses. Well, the thing is that U2 transcend a musical business and they also transcend an art project and a political project. They met each other at school when they were just 15, 16, Bono's wife and Larry's girlfriend were there too at that early stage, their friends at school are still their friends. They have overcome difficulties and supported each other at their worst moments, when one is in need, the others are there with him, we don't know everything in their lives, but just a few examples which are public: when Adam had problems with alcohol Edge was with him in the clinic, Bono spent a long time with him to support him after leaving the clinic, when Edge's daughter was ill they all stopped the tour without thinking about the money but the little girl, recently all three: Adam, Edge and Larry spent great part of June and July with Bono while he was recovering from his surgery, they are family, close family now, they celebrate together, they even spend part of their holidays together. I don't mean that they don't face difficulties among them, I suppose they do, they get angry with each other and so on, but it is like when you get angry with your brother or sister. That's in my opinion what makes it imposssible for them to continue as U2 if a member of them leaves.
If in the future one of them leaves the band, I expect Bono and Edge to continue making music, just because it is their way to express themselves and communicate, but it would be as "Edge and Bono", not U2.
There are also many religious and political connections among the members, apart, of course, of the music and business, that you will learn about if you have the patience of visiting us or reading on U2.
I'm only an ocasional fan of Guns'n Roses, I don't know much about the history of the band, but I think the relation among its members can't be compared with that in U2 and that's what makes the difference.
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But i love all 4 lads,
