These orcs are looking suspiciously like Bad-DM brand suicide orcs. 'no guys, he killed John's character cause he knew that you could heal him after the fight it's totally in-character'.
Speaking from a psychological perspective, it takes an absolute BUTTLOAD of motivation for someone to throw away their best chance at living. So why is this orc wasting it's action shanking a downed foe while angry PCs are stabbing it multiple times in the brain? If it's dying (0) and knows it's going to be killed, it might shank a dying PC just out of malice. If all the 'action' is heaps far away, it might take the time to outright kill a fallen foe.
Anything else and you're going into 'hur the orc knows it's going to die so it kill the PC so the PC doesn't get healed after it's dead'. Which is just.. absolutely silly. Humans don't do that, ergo, orcs don't do that. And if you have campaign-specific fatalistic angry orcs that do that, well, that's great, i'm happy for you, but that's not the general rule. Which is what we are talking about here.