I always DM with Risk vs Reward in mind.
The first time a PC does this (and it has happened) then cool you win. They surrender. Now what are you going to do with the 3 Orcs? "we tell them to go home" this is their home. "Oh, we tell them to screw off or we'll kill them" Hmm ok they run off...
I found that many of the solo battles just didn't live up to my expectations and I had to mod them on the fly.
Stuff like adding a wave of minions to distract debuffers.
Or upping the recharge rate of interupts.
Unlimited hp until i felt the players had enought. Don't knock this. If done...