Cutscenes are non-applicable. The fundamental concept of a cutscene in gaming is a non-interactive cinematic or cinema-style sequence.
Anyway, the idea of buffs wearing off is realistic, but not fun. Last I heard they were leaning more toward sustained buffs similar to Dragon Age's than toward a time-limited buff that has to be recast constantly, because they're using a Dark Souls style system of a certain set number of casts between rests.
While I myself dislike the idea of buffs wearing off during dialogue, it could actually prove to be an interesting add, provided that your enemies suffer the same disadvantage. So entering the hall, seeing this big bad boss having half the shielding spell arsenal casted on him could be made weaker by having a good long stalling conversation while your enemies buffs wear off. Would add to highly charismatic/speech centered character possibilites IMO.
And that'd probably mean that an *attack* option would be included in the dialogue, so maybe if you tire in the middle of the long dialogue, lulling the big boss in the sense that you're actually wanting to have a talk, to hear the evil plans or so, and have then a brief advantage in the form of hitting chance and wounding chance when you suddenly stop talking and decide to attack.
NPCs don't spam buffs while not in combat so far as I'm aware, especially if they have a limited number of casts and can't ever rest to recover the use of said buffs, so it wouldn't be a likely scenario.
Edited by AGX-17, 07 February 2013 - 02:18 PM.