1) Nothing in the epilogue for the PC you romance says you're together all the time on every single adventure the rest of your lives with ANYONE. So please, even IF Ali/Leliana/Zev are not in the expansion, don't assume without knowing this means that they're gone, or dead, or your choices didn't matter. Unless they change the epilogues, that just is not so. And if they do, play it through with a new PC and leave that ending for the old one.
2) Even IF the romance partner isn't joinable as a full party member all game long, there's nothing to say there can't be conversations or something else to allude to the relationship. It is a LONG leap from saying "This NPC is not in the party" to, "we're re-writing the story to trash your choices." Why do people insist that 1=2?
3) Oghren is NOT confirmed. You can make a red-haired dwarf pretty easily. But even if he is, if you're going down the Deep Roads, who else would you take? From a story perspective, it makes sense. But we don't KNOW it's Oghren yet. So speculating without confirmation is pretty silly.
4) It does say something about the quality of writing that people are all wrapped up about losing their pixel romance partner.

And yes, Leliana makes me melt too. hehe But as long as I don't see what happened to Aribeth and Sharwen in HotU, I'll be fine. And given the amount of time invested in the characters of DA vs those two...I think it unlikely that your romance partner is going to be thrown into a ditch. Most likely you'll see them or chat with them or maybe even have to save them from a disaster, who knows?