That wouldn't "prove" reality to anybody. Consider the possibilities:
1. He is not killed. Thus he has "proved" that jumping 12 floors isn't always fatal. Thus he has proved nothing, in an absolute sense.
2. He is killed, and is simply extinguished (i.e., no life after death). He has proved nothing, because there is no intellect to acknowledge the proof.
3. He is killed, and ascends to an afterlife. He has proved ... well, what? At best, it'd be something that is not part of the reality you're trying to evoke in your question. So again he's proved nothing.
And as far as you're concerned, you have no proof that anything has happened at all -- so is it really "proof" in the scientific sense?
Further, even if we assume that he has "proved" something by his jump, it is not clear that he has proved anything about "reality." Again: his point is about the inadequacy of human reason and senses to completely address "reality." What, precisely, will his putative death have shown about the nature of "reality?"
The thread is from 2003.
He is likely a troll.
He said it is impossible to know reality.
Gravity was mentioned, 'is it real? How do we know?'
Easy, step out the 12th floor window.
Now, let this thread from 2003, and the two people resurrecting it, die in peace.