We test rolling over the entire stack to another AWS DR region (just one we dont normally use) from S3 backups, etc. We do this annually and try to introduce some variations to the scenarios. It takes us about 18 hours realistically.

Documentation / SOPs that have been tested thoroughly by various team members are really important. It helps work out any kinks in interpretation, syntax errors etc.

It does feel a little ridiculous at the time for all the effort involved, but incidents like this show why it's so important.