when things go wrong, as they sometimes will... does anyone have a clue what to do? Nope. Craziest thing youll see all day

My two thoughts are, let it run out of fuel, nothing else seems likely to happen.
Or, if you must stop it, and why? Then maybe a 50 pound CO2 fire extinguiser dumping CO2 at the intake would cause the air mix to be so weak on oxygen that it would snuff out the ability to have a burn in the cylinder. That's only true though, if there is no nitro.
Yup, stick with number one response. Let it go, it's not seeming to do anything dangerous spinning the wheels, and will run out of fuel.

But geez, ain't there a kill switch the driver can reach, or one on the roll bar for track workers?

That caption/ title comes from a poem by Edgar Guest

 When things go wrong as they sometimes will,
When the road you're trudging seems all up hill,
When the funds are low and the debts are high
And you want to smile, but you have to sigh,
When care is pressing you down a bit,
Rest if you must, but don't you quit.
Life is queer with its twists and turns,
As every one of us sometimes learns,
And many a failure turns about
When he might have won had he stuck it out;
Don't give up though the pace seems slow--
You may succeed with another blow,
Success is failure turned inside out--
The silver tint of the clouds of doubt,
And you never can tell how close you are,
It may be near when it seems so far;
So stick to the fight when you're hardest hit--
It's when things seem worst that you must not quit.

- Edgar A. Guest