Not really I find karya surviving without any changes to canon implausible and you seem to be set on shirou having no change
I never said there wouldn't be changes to canon. Sakura certainly wouldn't be visiting Shirou's, for example, and neither would either girl have the same crush on him that they have in canon (because that came fundamentally from how unhappy they were with their lives). I just don't think Kiritsugu would tell Shirou to keep away from the Tohsakas.
In canon he deliberately avoided telling Shirou anything
, in the hope that he'd just forget about magic and move on. I see no reason for it to be any different here, particularly since the Tohsaka
family head died in the Grail War. Kariya might be around, yes, but he's not the head of the Tohsaka family, and the Second Owner of Fuyuki is still Rin.