I find that when I die sometimes my C4 stays put and sometimes it's gone, but I can't be sure without any controlled testing.
It seems to me that if I put C4 on the ground, then die, I can still blow it up once I respawn.
But if I am killed after placing my C4 on an enemy vehicle, once I respawn I never am able to kill that vehicle by using my detonator.
Does the game remove them upon death only when they are placed on enemy vehicles?