@TheLastTLK
What would they even do after?
The only thing I could think of is getting involved in the magus community in Illyaverse.
If that happens, maybe we'll finally see Illyaverse Kiritsugu.
On that note I really hope Miyuverse Shirou comes with Miyu back to Illyaverse and meets with Kiritsugu.
Shirou gave up his goal of becoming a hero of justice for Miyu's sake while Kiritsugu gave of his goal for the salvation of mankind for Illya's sake.
I bet they would have a lot to talk about with each other.