I find that players in warp pvp tend to log off when driven into a corner, and that this ruins the pvp experience. It's not like you lose items or anything, since keepinventory is on in pvp, but people still log out when about to lose.
Not really a way to prevent logging out - most combatLog programs will simply have people die when they log out so I'm not sure how that could be done - but combat logging in pvp warps is annoying true
Im in what teddy says since combat logging so is quiet complicated to some server dealing it, but it is intrinsically illegal doing a form so logging out while in combat. While there's another option for a player to do /spawn rather than logging out.