Take it. A real 100k is much more useful than an imaginary couple of million; they probably can't afford any more; there is still a very strong chance they won'

Take it. A real 100k is much more useful than an imaginary couple of million; they probably can't afford any more; there is still a very strong chance they won't succeed (as you noticed); and even if they do the VC will get their liquidity preference out before the founders see a penny, which they may well not do. Take it and move on.