Terrorist robots dissected - anatomy of a scare
DIY cruise missiles - not as easy as you think
The RF signals/EW battle is one that terrorists will really struggle to win. Lose badly enough and you won't just fail - you'll be traced to your remote piloting location and the next thing you know you'll be hip-deep in SAS men. To be honest, roadside emplacement would probably work better - perhaps that's why people tend to do it that way.
Even a nice simple GPS autonomous drone - if you could somehow make it strike hard enough at a reasonable price and size - can be jammed or spoofed without difficulty. It isn't hard to blot out or degrade the genuine civ-GPS signal within a smallish area, and the level of inconvenience to those nearby isn't all that great. It's not like drowning out hospital beepers or something. And the nasty old western forces aren't bothered at all, because they can use the encrypted military GPS signal.
Frankly, if GPS drones ever seem likely to become a threat, you can expect cheap simple GPS jammers at every target location. This sort of thing is one reason why a Tomahawk cruise missile costs hundreds of thousands of dollars, not $1k. (The other big factor is the need to lug a big warhead and lots of fuel.)
GPS deathbots aren't likely, though. Not soon. Terrorist cells which can make or obtain 50lb of reliable explosives, build them into a $60k robo-aircraft without blowing themselves up, and then operationally deploy the system by lorry without being betrayed, are quite thin on the ground.
If this was the heyday of the Provisional IRA, you might want to think about those GPS and RF-video jammers; but it isn't. The new kids on the block aren't in the PIRA league. They operate in UK organisations typically 10 strong or less - probably because they don't have solid community support - and it's a big day for them if they can make risky-but-functional TATP backpack bombs. Mostly they aren't even that good - indeed, they're often almost comically inept.
Even if PIRA were back, so what? Accept a little bit of GPS jamming around obvious targets, and get on with life.
Once again, it seems that the main thing we have to fear is fear itself. ®