Not positive, but I think if it's a nitro vehicle you can have a throttle return spring. Seems the spring would need to be strong enough to overcome a dead servo, but not so strong as to overwork a live one.

If it's electric, about all I can think of is developing a close relationship with a Higher Power!

But more seriously, I'm not sure, I don't use a receiver batt, but I think the speedo would shut down the motor if it lost signal from the receiver.