Unity walked back from charging per installation earlier today. Now they will be charging per device it is installed on.
It doesn’t solve the core problem, but it at least prevents install-bombing like you are suggesting
https://www.eurogamer.net/unity-backtracks-slightly-on-plans-to-charge-developers-for-game-installs
Be sure to make regular backups of your data.
… and using RAID is not a backup.