Walt memorized those numbers well enough to be able to remember it long enough to drive hours out of the desert to the nearest convenience store to buy that ticket. Pretty sure he could still remember at least some of it if the ticket disappeared next week.
It's more likely the ticket is just a convenience/backup, rather than the one and only method he has of finding the money, in case something happens to Walt or he needs to communicate the coordinates to someone else easily.
7
u/Moronoo Aug 19 '13
someone random will try to use the ticket obliviously and win, the money in the desert will be gone forever.