Ah, OK, then Rider will probably be OK with him.
Also, Sakura actually does learn to use magic post-HF, I think. Certainly she is learning in HA, and the version I am playing is a reasonably competent magus. She might be fairly helpless at the time of the game, but there's no indication that she would remain so once Zouken is out of the way (and, Zouken is a problem she simply is incapable of fixing herself).
Also, my Sakura won't be that different from what he knows as far as I can tell, aside from having Shirou around full time. She's close to Rin, and whilst she's not a proper magus in the sense that Rin is (because she has no desire to be), she is a very competent magic user (especially with her extra prana supply).