Of course you could try calling Roadside Assistance and see what they suggest. Another option is doing a "hard reboot." I'm assuming when you say you did a reboot, you mean you held down the scroll wheels until both screens went black and then they turn on again. But there is another reboot:
-Put the car in PARK
-hold down the buttons above the scroll wheels for 30 seconds
-then hold down the scroll buttons and do the typical soft reboot
-then go to Controls -> E-Brake and Power Off and select POWER OFF (click it again to confirm)
-then wait a couple minutes (be sure to not touch the brake or open the doors during this entire process)
-after 2 minutes, press the brake pedal and open the door and the car should come back to life
It's possible this process will restore your 4G.
There is more information here:
Re-boot your Tesla | Tesla
In that thread they mention depressing the brake pedal while holding down the buttons above the scroll wheels but I haven't found that to be necessary.
You could also try googling "Model S hard reboot."
Good luck.
Thanks.
It turned out to be an issue at the telecom provider, KPN for my car.
They've had a blackout and apparently it took some time to restore their systems.
Now everything is up and running again.
I will PM you later , after the trip.