I see someone's been looking into that new ABC show, Lucky 7, eh?
For me, it would depend. Basically, if I found I had the lucky ticket, I would not say anything and see if the person pays me what they owe (assuming they needed to wait for a paycheck). Since in your scenario, they've been doing this for weeks, the person who was borrowing most likely had every intention of contributing, and had the money never been won, would have eventually paid their half. So I would have no issue honoring that unwritten agreement.
If it was someone who was constantly "borrowing" money and never paid it back, I would probably have a different take on it as they really were not contributing.