As both DM (other people's characters) and player (my own characters) I've had characters decline revival, but almost never due to their death being particularly heroic.
I can't really speak to my players' reasons for declining*, but for my own characters it's usually one of three things:
The character, in character, has had enough and just wants to rest in peace
The player at the table (me) realizes this character's not going anywhere, so time to try something new
The character knows s/he doesn't have the resources to afford revival (it's expensive in our games) and refuses to go into debt
Most of the time I'm happy with my call after the fact. (note: your use of the term "retiring" is confusing; to us a retired character is one that is still alive but for whatever reason no longer being played)
* - except one: the character, a Necromancer, actively wanted to find out all about what it meant to be dead; and what happened thereafter. So, he declined revival when first offered; then a few weeks later accepted it when offered again. He was thunderously disappointed to realize that the revived have little-to-no memory of what happened to them while dead.......