You seem a bit undecided. 
So you want an end and don't want one at the same time. Considering that I think BioWare did great. I don't feel Trespasser gives us an end to anything. Solas leaves, yes, and he explains himself a bit. But it is completely up to your imagination what to do with this. There's nothing final after all. He will be back, his way will continue (and can take long), and even the relationship isn't definitely over. A thousand things might happen in the future. There are no bridges burnt, we can always turn around and go back. They skillfully avoided any decisions that mean hard cuts. They even let the inquisitor learn about him in Trespasser, so there's nothing standing between them anymore. They might not show it explicitly but for the roleplayers everything is an open playground and they can do and make up and roleplay whatever they wish.
That's my point.
I want to know the end but I don't want it (as a whole) to end. I'm not saying that this is the end of the story, but it is the last DLC of DAI, this particular story within the overarching Dragon Age story is over, even if elements from it carry over, even if they are significant ones. I like that about DA, actually, there is always an element of continuity while still breaking from the previous story. As I said, I liked the ending, very much so - it didn't evoke warm and fuzzy feelings in me, but that doesn't mean I cannot appreciate it. Nor does that appreciation mean that I do not want more, as you say, from a design standpoint that's actually a good thing. (It's still miserable to live through, though.)
As for roleplaying it... I don't find that satisfying in this instance. I like my stories to be on the same playing field at all times, if I roleplay a game, then I want it roleplayed from start to finish, if I play a video game, then I want all the story to be in that medium. Anything that doesn't appear there overtly is just a bandaid patch-fix over any wounds the game might have created. It just doesn't work for me otherwise unfortunately.
I'm not sure I agree. We might not play the same character again (who knows after all, maybe they are bold enough to copy GTA5 and AC Syndicate and have us play multiple characters) but they can still bring her back and continue the love story. They didn't do such a splendid job regarding Hawke or the Warden, since we only got a few sentences about/from them. But they could actually provide us with the means to add to our past experiences without sacrificing new protagonists. Like give us one (optional) mission in the next game where we play our inquisitor again, meet Solas, influence their interactions etc. Switching characters isn't too uncommon after all. Something like the Witcher did would work great to continue the past inquisitor's story without giving up on a new main protagonist. I feel the freedom DAI left us with is so much stronger than anything DAO or DA2 gave us.
You know, I kind of miss having more recurring characters. In ME I was always so pleased to see the evolution of so many of my friends and LI's, I kind of miss that in DA - but I am adamantly supportive of having more new and shiny characters fill up those spaces, so the sentiment isn't too strong. I'm thinking more along the lines of specific characters getting a little more screentime, since they went to all this trouble to have us be invested in their fates.
I'm sure that Solas/the romance will continue, I didn't mean to imply otherwise. But DAI's story is still finished regardless - anything that comes after will be an entirely new chapter, a new story in DA, it just won't be the same, it won't be the "main plot". I wasn't nearly as invested in Hawke's fate once I stopped controlling her (or him depending on my PT). Hawke's story is finished, we just add a tiny epilogue and it feels much less personal. I'm afraid that there isn't a lot of room to expand on that for the Solas romance, either, unless they actually do bring the Inquisitor back as the controllable protagonist, even if briefly.
Hey, I was thrilled the first time I got a reference out of Alistair about my character - and then after a while I stopped caring, her story was finished and that was that, even though I was deeply invested in her LI progression when I was actually playing DA:O. They need to work on the quality of the continuity presentation, I guess. I am hopeful, though, considering some dev comments about Solas and future DA games... I'm just apprehensive that my character won't get nearly as much love. (And unless my DA4 protagonist can romance Solas also, it won't have the same feel for me beyond the same satisfied/disillusioned volatile mix that Trespasser already gave me.)
Well, may I be wrong. I hope I'm just being paranoid.