If you sell your soul for 1 million dollars, and never get the money, does that prove there is no Satan?

No mainly because there is a big loop hole in your question you didn't specify it had to be in one big payment or in a certain amount of time or the means in which it is obtained so technically if you earn 1 million dollars in your life time by working then Satan would have kept his end of the deal. This is of course if Satan and God weren't just imaginary beings.

Also the absence of Satan wouldn't provide evidence against other Gods as a lot of them have no relation to Satan e.g. ancient Egyptian gods, Ancient Greek gods.

No, it proves that Satan is a smart shopper.

You don't own your soul. It belongs to God, not to you. And Satan, knowing this, would not buy your soul from you because, well, that would be stupid on his part to pay you for something you don't own and so cannot give to him.

More importantly, the Bible does not say that you have a soul. It says you ARE a soul. A soul, according to the Bible, is the combination of body and spirit (which is not something that survives death, but is more akin to electricity for an appliance--in this case your body--it is like an activating force for your body). If either your body or your activating spirit is removed, then your soul no longer exists, because the term "soul" refers only to the combination of the two.

And for the record, this is not a philosophical question. One could count it as a spiritual/religious question, or one could count it as an economic question, but not a philosophical one.

I guess you gotta determine wether Satan is willing to depart with 1 million dollars first, cause if he isn't, then the entire conversation is moot.

Im not giving you 1 million dollars but ill gladly take your soul >:)

I just means that Satan has all the good lawyers.

Who would you sell it to, in the first place?