I haven't seen a Death Knight in ages, let alone fought one, but I'd think that if they were constantly the cause of heartbeat loss bug reports and combat-error logs would be filled with messages about them.
Darkemud has a long and storied history of never replacing things that are "removed until..." If something gets removed to be fixed, rather than fixed and updated, it stays removed. I personally don't feel that this is the best option at all. If they're bugged, they should be repaired or replaced. If they can't be repaired in good fashion, whatever functionality they have that's causing the problem should be replaced with something that's of equal power and not causing problems.
I've had CPR work on players and runes both.