I understand the after Desert Storm the US military started using civil GPS units, which is why the turned off the "dither". I think that GNSS is here to stay as a robust system.
Furthermore, there are now 3 GPS systems. The US GNSS, The Russian GLONAS, European Gallileo as well as Indian & Asian networks under development.
I don't think there is a lot of concern about lack of availability. However, there is a well developed ability to jam GPS signals in local areas. I think this is what you can expect in areas of conflict.