In
that case, the canon of the
Harry Potter novels would be
just that - dropping the Trinity, at least, back into TYPE-MOON cosmology, but circa
1998. As such, Shirou and Ilya would be 7 and 8 again (and Ilya
WOULD NOT be happy about it), Kiritsugu and
Shiki would retain their Trinity memories, having used the Kaleidostick before (as would
Rin), with Takara theoretically not due to be
born for another three years, and Galen MIA, since he only
ever existed here as a
Servant . . .
Then again, the Hallows
have, in other potential timelines, shielded their masters from dimensional jumps; the Wand "duels" the ill effects (and wins, of course), the Stone anchors the soul and recalls it from Death, and the Cloak can
conceal one from them, so it's
possible that Takara and Galen can make the trip - sometimes, the effect can even be extended to
others, as well. And even if they don't
initially, Kiritsugu
knows the outcome of the War, and
Ilya knows everything
Galen knows about it, which is a good deal
more; at least
one Master (and Servant) spot can be
pre-empted . . .