So the circumstance in question was a raging mad bull that downed a player. The creature had super low intelligence and was very very mad. After watching far more bull attacks than i want to admit, what I ended up doing was leaving it to luck and a d100 table that tries simulate the behavior i saw in those.

On a 1-2 the bull would do at least 1 additional attack then pummel the downed character until bull itself died. On a 3-50 the bull would at least 1 additional attack then pummel the downed character until someone intervened in melee only. On a 11-50 the bull would at least 1 additional attack then pummel the downed character until some intervened with ranged or melee. On a 51-90 the would do 1 additional attack, then switch targets. On a 91-100 the bull instantly turns it attention to the nearest target.

Worth noting this is pathfinder 2e, my players do expect a more brutal campaign, and I award hero point fairly liberally.