Just responding to some of the posters.
I personally don't like this. We had a fight that went rather poorly for us, so I opted for tactical retreat. Others decided to be big heroes and stay... got promptly killed for their heroism, but woke up days later with a player missing an arm (no mechanical impact, as they made metal arm for him).
Besides the obvious that I'd rather kill a character than tear off one of my player's arms for a bad call, you mentioned the PCs were killed for heroism but then woke up days later. Was that the result of Raise Dead/Resurrection?
But I do get what you're saying overall, higher stakes required. That was my concern too.
edit: as for the OP example, maybe do not let the ranger just free kill bunch of orcs, might have made him overconfident in his capability to 1v1 the big bad guy, and overconfidence is slow and insidious killer
I should mention, it was the end of the session, and one of the players had already just left due to prior commitments, so I was wrapping up in a sense.
As a 5th level ranger and with the orcs (3) being bloodied I did not see this as a problem, besides I'm trying to get through swathes of material, and having to roll a bunch of stealth checks, initiative, attack and damage rolls against creatures that were under 10 hit points just would not be exciting for either the table or myself as DM.
I make the stakes clear at the outset of the conflict and, if the PCs lose, they lose (whatever that means in context).
How? I'm imagining you turn to the player saying, "Just for you to be aware, chasing down these orcs, alone, in an area your character is not familiar with (despite being a ranger), may result in the character's death."
Have I got that right?
@OP I don't know, I don't like how an NPC who ostensibly wasn't there just came out of nowhere and saved the PC. I'm not saying the PC should have died, but it seems more like you wanted to kill someone and couldn't make the math do it to the player, so you killed his friend instead.
You're right, I did not roll for the tressym's location, the only thing that had been established in play was that the animal companion had remained back at camp. I deemed it reasonable that it would anxiously be awaiting the ranger's return and perhaps be circling the encampment. Upon hearing the commotion (acute perception) it would rush out towards the disturbance.
I was indeed thinking of a reasonable cost to be paid for action failure and the survivability of the PC, whether it had to be someone's death, I don't know, it was what I came up with in the spur of the moment.