Well the odds of them walking away from The Elder Scrolls is almost zero... unless an Elder Scrolls MMO comes along and they go all BioWare/KotoR and abandon the single player series. That is unlikely of course since Bethesda Games Studio would not be making any possible TES MMO.
As for SHOULD they stop... I don't think so to be honest. I total agree with you about Resident Evil. I was a HUGE fan of the RE series until RE4... which was not a RE game as far as I was concerned. The story was totally different, the gameplay was different, and the enemy I was fighting were different. It was a different game series that Capcom simply put the Resident Evil name on to sale copies, which worked very well for them. However, I don't see that happening with TES. I mean for the TES series to change like RE did, it would have to basically turn into a Fable clone... and that isn't not going to happen. Bethesda seems to stick with what works, and simply add onto it or make small changes. Will there eventually be a bad TES? Sure. Its bound to happen if they keep making them... but just because one might be bad some day, doesn't mean they should stop making them just to "end on a high note". For all we know the next game would be 100% better then Skyrim, and the game after that might be even better.
So as long as the TES series is making money, I think Bethesda should keep right on making them... and I'm sure they will. We will probably see a rotation of Fallout and Elder Scrolls games for years to come.
if you thought RE4 was bad.......wait till you play RE5.
the problem is that bethesda doesnt make small changes from game to game.........they make HUGE changes from game to game and they havent always kept what worked in previous games. morrowind is almost a completely different game than oblivion in its core concepts from combat, spellcasting, quest directions, travelling, environment, weapon and armor systems, etc. i couldnt play very far in daggerfall cause of the graphics but from what ive heard morrowind was very different it. how many more skills can they get rid of. how much more can they streamline the game until it becomes a mere shadow of the games that started the franchise. i couldnt wait for the next RE game to come out after playing 1 and 2 and i hoped that they would keep making games like that forever.....alas how i wish they had stopped. its not just RE either. silent hill has gone down the crapper as well as other games that go on too long. very few games get better as they go along and usually those are things like racing games where they only tweak graphics and some settins hear and there.
as for fallout they could probably get some more traction out of that simply because fallout 3 is essentially an entirely different game than fallout 1 and 2. so technically we are only on fallout 2 right now with new vegas.
i also stand by my view that elsweyr and black marsh games would be disasterous. the only people that would like that are people that are already mesmorized with beast races to begin with. imagine almost every character you see is a hissing lizard or a khajit with their annoying voices...............that would get old after about 10 minutes to the normal person. better to stick with elven and human provinces.......at least you can relate to them.