I coup-de-grace PCs whenever it's feasible - like in the above. I don't understand this new mindset of "If I botch my save against the mob's Hold Person I'm out of the fight."
No, if you botch your save, the orc is going to behead you, if your allies can't get to him. Hold Person is Save-or-Die in the right circumstances for mobs, and it should be for players too.
It's the "one set of rules for PC combat actions, another for mob combat actions" that tends to make power-gaming prolific in my opinion. If the PCs can break the game, I will introduce mobs that do too, and thus parity will be achieved (even if I have to kill off the offending rollplayer so the roleplayers can enjoy the game.)
Besides that, it's the level of power of the enemies that truly determine heroism.
And one of the best moments in my DMing time recently was when my party, barging through a dungeon, found that Orc Sorceror who dropped the fighter cold with Color Spray (the fighter charged around the room to get to him and was nowhere near his party members.) For six straight rounds the party rogue managed to nick the nearby Orc with his crossbow and save the fighter from the Coup-De-Grace attempt, in one case hitting the AC exactly on.
The Fighter and Rogue remained really good friends for the rest of that adventure, I assure you.