Here's the lowdown -- the ingredients of the Sarevok's Remorse component are:
-- a dialogue between Yoshimo and the PC (starting with the line Xiao quoted), which should trigger [Edit: sorry, my bad] about one day after the
3rd original BW dialogue, which starts with "I have pondered what you have said about Bhaal. Could it not be that Bhaal intended to be reborn through his children?"
-- an extension to the Priest of Ilmater dialogue; Yoshimo's diary
-- a dialogue between Sarevok and the PC, in ToB.
@Anyone who's had trouble trying to get the Yoshimo-PC dialogue to trigger -- had you, by any chance, had the "I have pondered what you have said about Bhaal" dialogue before you installed UB? The variable would (or should, at any rate) be set there. (I'm kind of hoping this would be the source of the problem -- it still needs to be fixed, of course.)
If all else fails, using something like
CLUAConsole:SetGlobal("U!SYoshimoTalksPC","GLOBAL",1)
should work. (And if the dialogue still won't start, hit Ctrl+I.)
@Kara-Tur, Ilmater, and coiffure -- good ideas. I'll have to ponder on them when I'm awake again.