The bolded ones I would certainly agree with. Kirkian was one of the members of Quel'Lithien so I'd like to think he'd be the last high elf we'd see going back to Quel'Thalas. If he did, I wouldn't have very much respect for him, considering he was exiled because of his principles. It wouldn't look very good if he went crawling back after something went wrong.
Vyrin I'm not sure about. Her husband's story could have inspired her to rethink Silvermoon's direction since the Third War, but she's been a staple of early Alliance questing for nearly two decades, so I wouldn't want to spoil the picture by taking her out of it. Besides she might find it too hard going home without her husband. Staying away from Quel'Thalas might be the best thing for her.
Yeah, I think it's just an unfortunate reality for both sides in the equation and, as you say, it's understandable why Lor'themar might look elsewhere for political alliances. Especially when it makes for more geographical sense for Quel'Thalas to ally with forces with a hub on the same continent (if you remove the Forsaken wedge in between them).
I think that's a very astute assessment regarding Lor'themar's motives going forward. Quel'Thalas is rather isolated at the moment...
Absolutely. Being Sin'dorei is more a political/philosophical position, rather than making one part of a separate Thalassian ethnicity. Any high elf who returned to Quel'Thalas after the events of TBC would probably have to adopt the name blood elf (blue eyes or no) or they would rightly face deep suspicion and probably contempt.
Lanesh may very well be such an elf, for example.