Jebus Cross - 2.

And what if this happened closer to the finale—would the entire tournament have to be replayed?

I am assuming that only 1 round has been played and essentially the games don't need to be replayed; in the bracket, Antoshkin advances instead of Katrin.
Moreover, if a person is disqualified from the tournament, all game results are voided, and consequently.....

P.S. Yesterday Anton and I were reviewing the saves of his match with Katrin; we didn't have the strength for many days (it was 2 nights), but we managed to notice at least some questionable decisions (on the way, 2 hives are not taken, and the main army goes deep into the sands after a drowned one without scouting).