The signals will not be encrypted; SA will not be turned back on.
There is some concern that the Air Force is not keeping up with its planned schedule of satellite replacement. It is highly unlikely, however, that the GPS system will fail, or even become degraded. The satellites are being upgraded as well as replaced, even though an upgrade is not essential for system stability; it's the cost of upgrading that is most likely holding up the program.
The cost of maintaining GPS is a drop in the bucket compared to the amounts of money being thrown out the window by the government in so many other domains, so the problem is likely to be more one of proper accounting and administration than financial hardship or technical difficulty.