Maybe it’s hindsight seeing Worf in her position for all those years, but between the two of them, one of them would go eventually. They essentially played the same character; rough, kick ass, etc… Except one came with a Klingon backstory and one came with a tragic rape-planet backstory.
I don’t think (other than fucking data), there’s a single plot that they could give to Yar that they couldn’t also believably give to Worf from an emotional story perspective. They’re essentially the same character.