There's nothing you can do about this unfortunately. Make sure that you make active backups next time to ensure that this issue doesn't repeat.
Also, in future, I would recommend using /save-all in game as it works better.
If you want your server to support older versions, then you can use ProtocolSupport or ViaVersion. To use ViaVersion then you will need these 3 plugins:
- ViaVersion: Base Plugin
- ViaBackwards: 1.9-1.15.2 Support
- ViaRewind: 1.8-1.8.8 Support
Make sure that he is whitelisted by running the command /whitelist add (player). Also, make sure that he is using the latest version of Minecraft (1.15.2)
command /shop:
trigger:
open virtual chest inventory with size 3 named "Shop" to player
format gui slot 0 of player with cobblestone named "name" to do nothing # (for example)
Uninstall the plugin and restart your server, then use the Pardon command. Once that's done, you can reinstall the plugin. Take caution in future when hiring people, ensure that they are fully trustworthy.