What happens if a module is temporarily unavailable?

The event waits in a queue and runs once the connection is back. Nothing is lost.

Orders are written to the database before anything else happens — including when one of the modules is not responding at that moment. Order is preserved: events are processed one after another, not in parallel, so rules never run out of sequence.

The same holds during sales peaks. When orders arrive faster than you can refresh the panel, the system accepts all of them and processes them one by one.

You can check whether a rule ran on the automated actions list, which shows the execution history.