What I have assumed was going to happen is an "End of Magic" storyline. Dragons die, Brann dies, Night King/WWs die, Melisandre and all the Red Priests die or lose powers, and Westeros becomes essentially a low fantasy setting like it was in the beginning of the show, except permanently this time. Martin has hinted that the very nature of the north and the irregular winters is intrinsically tied to the white walkers as well, so that might also end.
However after last episode I don't think that will happen any more. I don't see Brann being in any more danger, and he would kind of have to die for this to work. More importantly, I don't think HBO wants to lose all that for any spin-offs that they want to set after the end of this series. Martin wouldn't have had a problem concluding his series with that when he started, but he didn't have millions of dollars invested yet.
I am honestly expecting a Happily Ever After ending, or something disturbingly like it. But it likely came down to a business decision, or which actors/actresses they could option for later.