I am not sure how my Lavellan is going to react. I haven't actually gotten there in the game yet. I rushed a bit through the main quests and did not balance out my play-through between side quests, companion quests, and main story, so I got to the point where the next main quest was the Temple of Mythal and I kinda got bored with all the stuff I had to do. So I when back to a way earlier save and now am working through the game trying to balance out the quests more, well at least between main quests and companion quest.
My sense is that she will not take it well. I don't really do multiple play-throughs with games like this because I don't really see my decisions being all that different from my initial run. Though I did start but never finished, an Elf-Mage play through in Origins where I was going to be more pragmatic and romance Zevran. I don't do "evil" choice characters, it's just not my thing. The reason why I see my Lavellan not handling the break-up well is because her clan has been destroyed (yeah I know I could fix this, but I won't), though I don't really see her wanting to go back even if they had survived. Between Solas and the Inquisition, she's not very Dalish anymore, and I already see her as being a bit of an outlier when it comes to her clan anyway. My headcanon has her and her twin sister (if I ever do go back to my orignal rogue archer play-through) as being something of a thorn in the Keeper's side because they would constantly ask questions and challenge any inconsistencies they found in Dalish lore. My headcanon also has the Keeper training both Enaris and Elleari as potential first/seconds, because they both had the potential to be mages but only Enaris' actually manifested. SO yeah, she's lost her clan, her twin, and now Solas has/will walk out on her- I really don't see this going well, but as to what she does specifically in reation to it all my brain hasn't gotten there yet.
In terms of JOH, which is more interesting in terms of the romance? post or pre breakup. After spending all of DA2 running around with Fenris, Varric, Anders, and Origins with Leliana, Wynne, and Alistair, I am finding it interesting that I don't really have a core group for this game. It's more like, okay who's the best to take with me for this area or this quest. Like my dragon slaying team is Solas, Cassandra, and Iron Bull- with Backwall thrown in on occasion just for mixing up banter triggers. The only real constant in my party is Solas.