Yeah, no one's limit breaks can be interrupted, but like any action in any mode of this game (even PvE), if the character initiating the action dies before the effect takes place, or the target is no longer targetable before the effect lands, the effect is averted entirely.
This is super noticeable with actions that have a long animation before the effect, from Hallowed Ground to Tornado Kick to Limit Breaks. It's extremely easy to die before you get any benefit if you use DNC's limit break improperly, but ones like RDM can be shut down before the damage and healing actually applies despite the instantaneous animation.
Even DRGs can get killed before they're untargetable from jumping. Timely stuns or pigs etc will also apply as they go skyward, and you can see they're still cc'd up in the air on the UI. Only difference between them and GNB is that once they're up there (and not dead from any hits that may have landed), they're safe.
Aoes even secretly hit targets in sequence, not simultaneously. So, boss enrage clears happen where the boss dies when 7/8 players get killed by the enrage. Theoretically it's possible you could have a SAM counter Zantetsuken 5 players and die after only killing 4.