Karl couldn't leave Cousins in for another minute to close the 3rd? Play him 42+ minutes if you have to. Gotta win games, unless you're alright with a 2-8 record.
He was barely making it up the court. And let's not forget he's coming of a sore Achilles.
21 points in 1 quarter? 45 more seconds isn't going to kill you, sore achilles or not. If something as serious as an achilles is truly a problem, you shouldn't be playing starting minutes in the first place, which he has been logging.
And if his Achilles pops in that 45 seconds, then what? It's the Thibs/D.Rose thing all over again.
The chances of that are extremely slim. 1 extra minute of extra playing time in one quarter for professional basketball player is nothing. You can always rest him the next day, or if you have a back to back, cut back his minutes slightly then. He's coming off of one day's rest.
If your medical staff isn't competent enough to evaluate a true achilles issue with medical diagnostics and physical evaluation, that's their problem.