Well, the N810 is basically the same in all important aspects to the N800 that the N800 is practically guaranteed support as long as the N810, which in turn is good as long as the N810W, which isn't quite launched yet.

While it is possible they stop officially supporting it, it doesn't make any sense with the similarity, and even if they do, it'll be pretty simple to hack the latest N810 builds for the N800; the touchscreen/sound controller are different models in the same series, for example, so rebuilding the kernel with different modules could be needed; nothing big. (And who even runs the stock kernel, anyway?)

As long as there are new N810 images, there will be new N800 images, whether official or community.