It's likely the additional overhead worrying about HA is not worth it, not to mention the real possibility of HA just not working properly in actual failure scenarios
It seems like his business could at least afford an HA setup on a cloud provider. Moving to any hosted db with backups, updates and redundancy could be worth it.
As for HA failing, it's still less likely than not-HA failing.
Also an HA setup allows for maintenance and upgrades without downtime, which is way better than the very common "we don't upgrade if it's working, because it could break".
Also there is a third option between HA (with its increased cost and complexity) and "we don't upgrade if it's working, because it could break", which is "take the site down for a few minutes, do the upgrade, bring it back up". It's not for every site, but there's a range of sites for which that is fine.