So, it may sound stupid that I'm giving up $100 with no hope of getting anything back. But that's because the counterfactual is stupid, not me.

(Disclaimer: I'm going to use the exact language you used, which means I will call you "stupid" in this post. I apologize if this comes off as trollish. I will admit that I am also quite torn about this decision, and I feel quite stupid too.)

No offense, but assuming free will, you are the one who is deciding to actually hand over the $100. The conterfactual isn't the one making the decision. You are. You are in a situation, and there are two possible actions (lose $100 or don't lose $100), and you are choosing to lose $100.

So again, are you sure you are not stupid?

And now I try to calculate what you should treat as being the probability that you're being emulated. Assume that Omega only emulates you if the coin comes up heads.

Suppose you decide beforehand that you are going to give Omega the $100, as you ought to. The expected value of this is $4950, as has been calculated.

Suppose that instead, you decide beforehand that E is the probability you're being emulated assuming you hear that came up tails. You'll still decide to give Omega the $100; therefore, your expected value if you hear that it came up heads is $10,000. Your expected value if you hear that the coin came up tails is -$100(1-E) + $10,000E.

The probability that you hear that the coin comes up tails should be given by P(H) + P(T and ~E) + P(T and E) = 0, P(H) = P(T and ~E), P(T and ~E) = P(T) - P(T and E), P(T and E) = P(E|T) * P(T). Solving these equations, I get P(E|T) = 2, which probably means I've made a mistake somewhere. If not, c'est l'Omega?