does the modern G.P./SUPERBIKE have a "dead man" type switch similar to the old valve lifter?

Im not sure about using a valve lifter as a cut off switch. though it would work. (excess oil flooding the lifter causing shut off)

Most if not all are supposed to be fitted with mercury switch cut off which is supposed to work if the bike is laid down. ( preventing it over rev ving. )

Doesnt always work !

its often tampered with to prevent cut off with a front end slide.

just so the rider can pick it up and continue.

The old valve lifter brings back memories, a lever on the handlebars that when pulled in holds the exhaust valve open so the motor stops due to lack of compression, it would not work on a race bike because the piston would hit the open exhaust valve and the result would be very costly.

Proc and Wiggysan have covered it well.

Like Proc says most GP bike if on their side for too long will cut off to save the engines.

The WSB bikes machine dont as they dont have stupid engine limits so can be started again or even ridden away at times.