I may feel bad about a beloved character dying, especially if it's one that's good for the story, but I never take it back. Ever. Players have to accept the consequences of their decisions, even if those decisions are made with incorrect information. You might try to give hints, but the player is ultimately responsible.
In my game a few weeks ago, the party is infiltrating the dungeons of an old Temple of Elemental Evil Stronghold. They don't know what's down here, but they've had clues that there are bandits and humanoids within. They fight a group of gnolls (average encounter), but two manage to flee. The party gives chase, even though they're too far behind to actually catch them. I (somewhat) subtly remind everyone of the Han Solo v. Stromstroopers scene in Episode IV, but they continue anyway. The chase ends when the gnolls lead the party into an ambush of Bugbears (hard encounter pre-ambush), who very nearly TPK. I felt absolutely no remorse, and was willing to let the party die for their stupidity. They didn't know they were going into an ambush, but they knew of the possibility of other enemies, and I even gave them a clue (even though it was somewhat hidden in OOC talk).
In my game a few weeks ago, the party is infiltrating the dungeons of an old Temple of Elemental Evil Stronghold. They don't know what's down here, but they've had clues that there are bandits and humanoids within. They fight a group of gnolls (average encounter), but two manage to flee. The party gives chase, even though they're too far behind to actually catch them. I (somewhat) subtly remind everyone of the Han Solo v. Stromstroopers scene in Episode IV, but they continue anyway. The chase ends when the gnolls lead the party into an ambush of Bugbears (hard encounter pre-ambush), who very nearly TPK. I felt absolutely no remorse, and was willing to let the party die for their stupidity. They didn't know they were going into an ambush, but they knew of the possibility of other enemies, and I even gave them a clue (even though it was somewhat hidden in OOC talk).