Actually, ifrit hm is doable even without someone stunning ifrit. Though PUGs would generally not accept it since the fight is a lot easier when it do get interrupted.
Personally, I never trust a random player when it comes to that so I move from eruption regardless if it got interrupted or not and I would advice everyone to do that.. That way you wont wipe if 1 gets through. Though it also depends on which one that gets through and where everyone was standing..

If you do not like that duty then I would suggest that you try to get a static party for ifrit instead and either have another pld with you that takes on that duty or just try to kill him without stun.