The plot doesn't matter. As long as people buy the games Bethesda will still make the series.
Wrong! The plot does matter especially in RPG games, are you daft boy? You must be new to this genre because plot and story are a huge factor in RPG's. If Bethesda just starts throwing out half finished products with little to no story that have nothing to do with how the Story as a whole has progressed thus far people will lose interest and ultimately faith in the company. What follows from there is obvious as there are only two things they can do.
Anyways.......
As many people before me have said, there is plenty more for Bethesda to do. I think that even if they hit a slight snag there are plenty of people on these forums who would be more than happy to help them along the way to a new release. There seems to be a serious wealth of information on these forums and some very skilled and talented modders as well as the lore specialists
. I don't think anyone here would allow for them to stop the series for the simple reason of running out of story or ideas.
I may not have liked everything that they did between the last 3 TES games (not including expansions only main games), but as a whole they seem to be on the right track here and I have faith that Bethesda will continue the series until all possible areas and stories have been explored and told.