This may not be technically feasible, and if not, I'll work around it somewhere. But I got it to work once, and I'm not sure why I can't get it to work again.
Basically, I have this archvillain that's not actually there to be fought - he's supposed to run away upon seeing the player, because now's not the right time to fight them. To that end I made him not required for mission completion, run away at full health, and run away with 12 (or 1 - I tried both) minions left. I tried this in both City Map 01 (Ruined) and The Zig Breakout, but in the former, he didn't run at all, and in the latter, he stopped and started attacking me once he saw me.
This was a particular kick in the face, considering I just ran into Agent Crimson with my villain and he very dutifully ran like hell without my being able to do anything about it. Is there any way to get my intended fleeing to work, or should I find a workaround for now?