I don't see why they shouldn't. So many other bands have reunited - Kiss, Def Leopard, KC and the Sunshine Band. Only time a band shouldn't reunite is if most of the members are dead, or maybe if they weren't any good. The fans would love to see Guns 'n' Roses play again. Their music was terrific. Old fans will go, of course, and they'll probably draw new fans as well.
It seems like everything, whether it be television, film, or music, is revolving around reboots and remakes. Why should Guns N' Roses be any different? I think their fans of all generations would love to see them back together performing, even if it's just to see if they "still got it."
It is a good idea for Guns 'n' Roses to reunite because the fans will enjoy the chance to see them perform live, which would be special for fans who have never gotten to see them live. Plus, if they created new music it would be fun for old fans and new fans to see how the band's musical style has grown or stayed the same.
While I generally think that old bands reuniting is a kind of depressing, I feel that fans should enjoy their favorite now-defunct bands. If the members of the band are open to a reunion, why shouldn't they reunite and give the fans what they want? They just need to be prepared that it might not sound exactly like it did 15+ years ago.