Odd, I was thinking the exact same thing when I re watched the trilogy some 2 weeks ago.
"Why have I not thought so much about that bag before."
It is interesting, and I wouldn't be surprised if anyone "up there" already have thought up something about it. Though, I would think that there is a great chance that the Trainman already took care of it and either kept it or had it given to the Merovingian, in one way or the other.