^They wouldn't. They have absolutely nothing in common. Yuu is not Sayaka's type. They can barely get along as a kouhai and senpai, regardless of the Touko situation. Without Touko they have no reason to ever meet or get closer either. I would reckon they wouldn't even have met. I can understand that clashing personalities are somewhat fun to pair up, but Yuu's case is far too special for this to work. Sayaka would never be able to awaken her feelings like Touko did. The scenario that would lead to this pairing in a Touko-free universe would be unbelievably contrived and then you would have to somehow stabilize that too, which is even less likely.
I have nothing against the pairing conceptually, it just doesn't work.
Wait... there are older arts for this...
BASE! BV REPORTING IN! I'M JUMPING RIGHT INTO THIS RABBIT HOLE! IF I DON'T RETURN IN HALF AN HOUR, CONSIDER MYSELF DEAD!
EDIT: 19 minutes later
BV reporting in!
Before you ask if it was interesting, let me tell you...
It's interesting. You don't see them together much in the series, but it's like they snap together like Legoes, before others or possibly they know why.