I suspect that would fall under the rule that if two black holes’ respective event horizons ever cross, they merge and initiate the eventual merger of the two respective black holes.
I've seen this vaguely referenced, but when I dig in I don't find support for it.
It's far from obvious that just because the event horizons (which is just a mathematical concept and a 3D area of space) should control the trajectory of the singularity.
With two identical blackholes, with a event horizon of radius R, why should a singularity 2R away be unable to escape?
