Dwemer return in the next DLC and then all the factions in skyrim had to fight them off slaying them all back into oblivion ?

Depends how they did it. It better be a pretty [censored] elaborate story.

Still play it? Of course, there are few games as good as an Edler Scrolls game.

Would they lose the last bit of trust I have in them? Yes, and I would be very disappointed.

If and only if they had a tone of VIABLE explanation backing it.
Fight them? Why? They are scientists bent on study, they have no reason to go and whack people.

I sincerely hope the Dwemer stay gone. I really do.

lets say they return from an oblivion gates owned by a daedric lord who has them belive they have squaters on the land of kyrim and must rid them of all the races and be dwemer land only reclaiming places liek markarth and the ruins and you had to go on a mass dwemer slaying spree cleansing dwemer ruins of the dwemer

Pretty much this. I dont know of any viable way they could make them return.
And I hope they never do.
The dwemer are so cool because their mystery.
End that mystery and you will ruin one of the best things of the elder scrolls since morrowind... forever.

Weren't the Gates closed by Tiber Septim's sacrifice? If so then they couldn't do anything with the gates.
As for them taking back Markarth...meh that's really the only place, sure there'd be a scuffle but I doubt they'd wage an all out war, no doubt they'd find some other way inside it and retake the place from the inside out.

I'd rather not bring back such a mysterious race just to off them in the next moment...

This sounds like a copy paste of the Oblivion′s MQ... which I really dont liked.... so... better not!

still be mystery cuz slaying them isnt going to mean your gonna learn anythign about them other than what colour they bleed

But just bringing them up without any explanation and without the possibility to interact with them... its just worst than the fact of their return itself!