There are two main scenarios to a permanent PC death: 1) the player wanted to switch characters for Reasons, 2) the PC's body is unrecoverable or bringing them back isn't possible.
For the first case, I would much rather the player come to me and say, "I'm not having fun with this character" or "I really think the party needs a healer" or whatever the reason is. The game's much better when everyone's having fun and continuity of characters' plots helps me as a GM. It's better, IMO, to tweak and adjust an established character (even going so far as to completely rebuild him) and leave his story arc intact than suicide the character, or just decline to be resurrected, for entirely fixable reasons. The story goes on, everyone has fun.
Obviously, if a player is steadfastly intent on abusing this and remaking their character every week, I'd have a talk with them. Perhaps they're looking for a different kind of game than what I'm running or there's some other underlying cause. I zealously avoid, as a friend likes to say, "playing with jerks" so it's never been an issue.
Permanently dead through in-game events is something else entirely. Sometimes, the dice just hate you. Or the GM rolls 17s all night. While I avoid intentionally putting the PCs in unwinnable, inescapable situations, random chance means terrible things are going to happen. When it does, it's a terrible event, so further compounding the sadness and hard feelings isn't productive.
I always bring in replacement characters, regardless of circumstance, at average level and wealth. If possible, the new PCs trades across the dead PC's gear for equivalent items. The dead rogue's +2 shortbow becomes a +2 longbow for the new fighter. The dead ranger's +4 armor becomes +4 bracers of armor for the new sorcerer. And so on. Anything that doesn't have a reasonable analogue gets liquidated and the player can buy something class-appropriate with it. The dead PC's gear then exits stage left in some RP-appropriate manner, assuming it still physically exists. This keeps the new PC at the same wealth and approximate gearing that the old one had.