It will last as long as “V” did.
It will last as long as Firefly...
It’ll probably do pretty well. It’s gluing onto a very successful movie franchise, that’s got a strong following. The only real question is how will they hook each episode, what are they going to be doing. But since it’s all under the same umbrella as the movies, and given Joss’ skill at building a bad guy over the course of a season, it’ll probably work well as a build up/ ad for the next movie.