Direct YVR-IST does operate but TK refuses to put me on the flight (claiming I booked a star alliance booking even though I booked directly with them!)

As for the third alternative, wouldn't that still be at the whimsy of the TK staff? They claim no such options exist but of course they do - for example YVR-SFO on AC (UA code share)

As for your first point, yeah it's what I suspected as well (my gut has been telling me this wouldn't end well for me for a while lol)...I just spent the last 5 hours with TK support and it all ended with the CS staff writing another feedback form (this time with a note of urgency included thankfully) as that rep couldn't see any flights whatsoever any more for my date (April 2).

I actually can't log into my (or P2's) TK account either so I wouldn't be surprised if there's some issue with the TK portal currently

Anyways, looks like the issue will drag another day or two at minimum unfortunately (doesn't help that I have a second ticket for P2 on identical itinerary booked via LM as well, which I intend to change to whatever TK let's me change my ticket to...and who knows when that change will happen)

P.S. I should also add, I don't have any flexibility on the date itself unfortunately as P2 is working the day earlier (while even a day later significantly spoils my overall itinerary as we're only spending 3 nights in Istanbul). Not that it matters anyways as a day earlier (and later) has even less options than my date (no direct YVR-IST TK flights for example)