The solution is to build in-house or to acquire the vendor for any systems you need to run synchronously inside your multi-billion-dollar revenue stream. Which doesn't seem unreasonable, and seems like a good motivation to architect that stream so third-party products don't have to be run synchronously.

If I read the comment right (a big if, I'm terrible at interpreting sentences that end in the middle with storm of dots and an implication), then he/she is implying that obviously we never considered running code asynchronously.

If so, this implication was inaccurate.

I’m not saying that it wasn’t considered, I just don’t know that a one time code audit offers sufficient downtime protection for me. If you’re worried about an external service being in the critical path then taking it out of the critical path seems like the only foolproof approach.

Not if it really is responsible for keeping billions of dollars flowing.