Dota is so community-dependent and IMO it can't have a lot of setbacks since there is no real big money behind it. And I think that HoN is a setback in the process of developing Dota, because it isn't in the interest of Dota to divide the community like this. And by community I mainly mean the people who are actually doing something for the game, like sponsors, sites and other organizations. Because I think they will tend to choose the newer shinier game over the original.
However most of the real RTS gamers(non-Pros) will keep playing Dota because they know the same thing I have learned over years of playing games: "Gameplay is king." No matter how a game looks or the side features it has, the actual gameplay is the most important, and here is where Dota stays #1. This does mean that all the new gamers will go to HoN because they actually care about graphics and such.