Lennon was so complex that these questions are impossible to answer with any certainty.  I think that he could have remained relevant had he wanted to, but I don't think he would have wanted to.  I think he would have disappeared.

I honestly don't think that The Beatles could have ever reunited to the point of moving forward with new music much like I don't think gnr can.  The differences between Lennon/McCartney are similar to Axl/Slash in many respects.  They weren't just professional differences, there are personal issues as well which complicates things further.

This is the coolest chat option I've ever seen at a forum.  Great job everybody!

There really is no comparison.  Axl Rose, while a very talented musician, is not in the class of the timeless legends.  He holds up better against his peers, but even there Cobain, Reznor and others were far more influential.