I love this Marina Sirtis interview I heard on some podcast, where she pushed back hard on the idea that Tasha had no development in season one and asserting that if she had been in that role, Tasha would have been on the show all 7 years. She also talked about the "too many women" thing and how close she came to getting axed, before things went awry with Crosby and McFadden in other ways.
Troi is my favorite TNG character, and I always attributed most of that to Sirtis herself. That was the luckiest casting choice they made, that character played by a less interesting actress would have been a disaster. I definitely think the flip was a fantastic choice, but I also think it would have ultimately shaken out fine the other way, in that I suspect I'd have loved SirtisYar as much as I loved SirtisTroi.
I'm sure if they'd cast Crosby as Troi, she would have been gone at the end of season. It's not like the writing for any of the characters was that different, quality-wise. And with the writers obviously struggling with Troi, the actress being unhappy, and the producers feeling the show had too many women, what would have kept her around?
My suspicion is that Sirtis-as-Yar would have ultimately landed the same place Troi did (in the series)... paired off with Worf. And those two characters could have made much more sense together.