> What happens to a GPS after August if it can't roll over?

Maybe it plays dead?  :-)

Actually, the biggest problems seem to be:

1)  reports wrong date

2)  takes longer to cold-start (and maybe even warm-start) because
    the ephemeris data doesn't match it's idea of the current date

3)  some units apparently can't successfully cold-start at all, but
    apparently there aren't many of these