Had a similar thing happen when I did the HSC in 2020 (Australia, New South Wales version of SAT I think? Big exam in your final year that gives you a score for universities).

I was halfway through my legal studies HSC exam when our school got a bomb threat called in, so the exam had to be cut short and the entire school evacuated to our oval. We couldn't continue with our exam since it'd had already been interrupted and the entire state does it at the same time, nor could we redo it cos it wouldn't be fair to us.

I was told the markers would give us a score based upon the exam answers and essays we wrote so far, and our assignments and exam grades during the year. Worked out for me, I got a 96 for that exam!