If material reaches the Von Mises criterion, material yields and theoretically part supposed to be destroyed. To calculate allowable working load limit in Mechanical Engineering use FOS (Factor of Safety):
That's why we utilize safety factors. Here we will commonly use 3:1 based on YS keeping well below the proportional limit. If I see a stress that approaches the YS I get antsy. Remember also that the default stress reported is node-averaged not element averaged and therefore usually might be higher than reality.
And aren't engineers supposed to be grumpy?