Soul Reaver used Blooddrinker to create an imperfection in the barrier and is now using a Dispel Magic spell to unravel it completely.
If there is no one actively there to counter his attempt, it'll come undone pretty quick.
If there is someone who is actively maintaining the spell, it'll end up being a sort of mental duel between them and Soul Reaver as they try to re-knit the enchantment that Soul Reaver is trying to undo. Soul Reaver's very practiced at these, but I don't know who or what he might be up against.
In either case, Blooddrinker will also drain the barrier dry at some point (how quick depends on how much energy it has, and if it's being fed more from somewhere) unless something can replenish the energy as fast as it's being consumed.