I don't see urban fantasy going away. Like any other genre, it has a large audience base. Like any other genre, a work's success is going to be based on the story and characters--does the book draw the audience in? But because the market is so flooded, word of mouth is probably incredibly important as well. But that's the case with any book anyone writes.
I think what might be more detrimental and beneficial (yes, contradiction there) is the e-reader market. The problem is that now the market is even more flooded with books, short stories, etc. and a lot of them make you wonder who told the person they could write (okay, that was very snobby, but most of you have probably read those e-books that have literally no editing whatsoever, no character development, bland story, etc.). These factors are the downside--a flooded book market overall, with much crap to wade through.
The plus side? It's probably easier than ever to get published since there isn't a lot of revenue involved in publishing an e-book. I also noticed that many authors offer their first books at a much discounted price in order to build up an audience--then the books get progressively more expensive as they build that audience base. It's also very much looking like if you want a physical, print copy of the book published, you're going to need to achieve a certain amount of success digitally (sorta the same way paperback to hardback always worked).