It still takes V out for a round, as V has to cast dispel-magic to full-size Bloodfeast, and Miron is of at least comparable level to V (and could easily be higher), making the caster-level check quite difficult.
I'd probably just go for dismissal if thinking tactically, OTOH, this is a webcomic, not a D&D tactics seminar, and as a webcomic Bloodfeast smashing the forcecage from within could be quite amusing.