Probably the biggest reason that DisneyQuest is doomed (longer-term) is that the economics for it were predicated on being able to replicate the "high-end" games across the country. A pretty good amount of R&D was put into developing the VR and other games there. The thought was that they could keep DQ fresh by updating the games at the various locations over time, amortizing the design costs over all the locations. With Orlando being the only outlet, though, there's no more Imagineering work (that I know of) devoted to this area, and the single site probably doesn't bring in enough $ to fund any further development.
That's not to say that there's necessarily a short-term issue. It's almost certainly profitable now, or they would have closed it. It can probably go on for quite a while with just standard maintenance, and updating the "standard arcade" games. However, over time, the higher-end games are going to fall into disrepair/become outdated, and there won't be any good replacements ready for them, nor the income to justify spending larger sums of money for major repair, replacements, or design of new games.
I love Disney Quest, and would hate to see it go, so I hope I'm wrong, but I don't see any way it can really survive long-term. I would expect Disney has some plans ready for whenever they decide that it would be more profitable to use the location for something else.