So in other words, not like a loan?
An advance is "like" a loan because in both cases, the money is expected to be paid back by the person or group of people who receives it. There's lots of differences. Repayment terms. Exit clauses. Interest rates etc. But seems pedentic to say that the advances offered to musicians are not like loans they take so that they may have a claim on the future revenues of the sales produced by their work.
It depends on your contract. Usually, poor sales won't result in needing to repay an advance. However, there are plenty of other clauses that the contract could contain that would lead to the contract being canceled and potentially the advance having to be repaid (due to delays, editorial disagreements, poor quality, etc.)
I'm sure there are many, many other musicians who took a similar risk that didn't pay off as well as it did for Satriani