I don't take iffy shots. Even the near-perfect shots can provide iffy results. I keep my shots on game animals (eatable) to reasonable distances. My rule of thumb is any distance with 15 inches of drop is the max for that rifle. I will push the envelope on Varmints.
I took a broadside shot at a Roebuck, maybe 70 lbs., at forty yards. A near perfect shot a couple of inches above his heart. He took off like I'd burned his rear end, up a steep slope. I got ready for a second shot, I figured he'd stop to blow and check his back trail. When he stopped at maybe 125 yards, I put a second shot into him broadside quartering away. He ran another thirty yards. When I skinned him I noticed two bullet holes an inch apart. His heart looked like a bowl of chopped up Jello, it kind of dribbled chunks between my fingers when I picked it up..
Plan for the worst, hope for the best. IMO iffy shots are going to give you iffy results, even near perfect shots can result in problems on occasion, IMO you have an ethical duty to put an animal down dead, as quickly and efficiently as possible.