It’s astounding how often people conflate advances and loans when talking about the music industry. If anything it’s closer to seed capital than a loan.
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