Ever? Based on the advances seen in the past decade or so, full autonomy is coming. Whether next year or 20 years, I'll admit I don't know, but the day is coming. And yes, eventually people will be riding in fully autonomous aircraft (albeit first in cities before combat).
When you say the enemy has an "off button," what are you talking about exactly?
Yes, control signals can be jammed. Pretty soon, the technology will be there to go fully autonomous for most missions, so that there won't need to be a SATCOM link to Nellis. Whether that's ethical or not, who knows, but it's going to happen eventually.
If you mean that they can take over the aircraft controls by a virus or something similar, then they can do that in manned aircraft just as easily--the next generation of manned aircraft are all FBW. They don't have backup bell cranks and cables.