Hi,
We’ve provided a FLOSS migrator to get you off of MySQL. It works with SonarQube database schemas 6.7-7.8. I suggest you upgrade first to 6.7.7, then run the database migrator, then finish your SonarQube upgrade to 7.9.2.
To your specific question, the upgrade to 6.7.2 should go just fine on MySQL; MySQL was still supported in 6.7.* and the database upgrades were written to work with it.
HTH,
Ann