Someone here wrote an excellent post about using "relationship Judo" to lean into your WAS's threats. If they threaten divorce you say "Great idea! That would probably make things better -- what's the first step?"

Don't let them hang threats over your head, just lean into it

Married 18, Together 20, Now Divorced
M: 48, W: 50, D: 18, S: 16, D: 12
Bomb Dropped (EA, D): 7/13/11
Start Reconcile: 8/15/11
Bomb Dropped (EA, D): 5/1/2014 (Divorced)
In a New Relationship: 3/2015