Hiya!
First of, let me preface by just saying...oh man, how I
loath "in-depth" meta-game thinking! Now that you know where I'm coming from...
Meta-Game Thinking: I have X hp's, it does X damage...is that less than Y damage he may do to me/my group if I stay put?
Character Thinking: Nope. That could kill me! Are you crazy? I have to find a better way...
Personally, as DM, I have used meta-gaming players that "meta-game" too much against them...usually with hilarious death of their PC ensuing. I don't feel bad at all when I do that. Not one whit.

[golum voice]
Cruel DM! It burns! It bites! It..freezes! [/golum voice]
Now, I don't just whip out the "I can meta-game better than you" card at the drop of a hat. It takes a LOT for me to get to that point, but when I do, my point is usually made; do what you think your character would do and you'll be better off. I, as DM, "place" monsters as they would logically be; I don't "build encounters" based on the PC's, I "build encounters" based on the game world and as the campaign setting dictates. For example, a fen that is known to be infested with goblins will be infested with goblins...even of the PC's decide to head in there and they are all 14th level. The goblins are about to have a
real bad day! If a mountain pass is shunned because of the rather savage stone giants that live in them...and the PC's decide to risk going through the pass, they can easily encounter stone giants...even if the PC's are only 3rd level. I don't factor in the PC's class make up, racial make up, or levels to any serious degree. A bit, sure, it is a game after all...a game that is hard to play when everyone is dead and constantly making new characters...but that consideration is secondary to the campaign as a whole. Because of this mentality, I believe my players can think "in character" to better effect than "meta-game" thinking.
Anyway...in the OP's post... *shrug*. I could see a brave and emotional thief risking pain, suffering and death for his beloved friends and companions, but I can't see a thief risking the same because the player is thinking "I have X hp's, it does Y damage; it's probably worth it...". I'd rank that right up there with "My guy kills himself after taking off all his magic items, telling the party to give it to the next thief they hire. Oh, here's my new guy, he's a thief...so he can join the party". >:|
^_^
Paul L. Ming