Just killed the Forsworn Briarheart and looted,and he didn't have the key on him,like hes supposed to have so you can open the tower. Is this a know glitch or something,and do i have to wait for respawns?

I really can't remember if the key will respawn on the Briarheart or not (after 30 in-game days), but sometimes if you somehow misplace the key the first time you clear a given location, don't pick it up, or it never appears on the boss to begin with, it may not respawn. Additionally, you do not actually need the key to unlock the door, it can be picked, but since it is a master level lock, it could be a bit difficult depending on your lockpicking skill.