greetings quatrain.
if you decide you must finish the quest, i would consider going back into level 2 and really scouring the entire level for the way down to three. they are usually there, just hidden behind walls, etc. also (not like you don't know this), look for any level areas still covered with the fog-of-war and explore these.
as far as the quest itself is concerned, finishing is not necessary.
the BFs are random and in a lot of versions other than 1.45, the merchants would/could simply change the quest during your time in the BFs - very strange if not frustrating.
i would have to imagine that almost all of us who have finished the game and also completed the BFs ended with at least one unfinished BF quest. i think i had 3-5 without counting the act IV BF6 thing. oh well.
i'm sure you know this too, the BFs are not necessary for the successful completion of the gmae. they're 'fluff'.
the best advice is to simply disregard it/them if you have a problem and continue on - but that may not be very satisfying to you.