Hi there, can we have a command to be run when the player no longer has the permission?

Using luckperms api in your own plugin, yes
Using luckperms, i don't think so

There is no reason for a perm plugin to have this.

Sorry, not something I plan to include in LuckPerms itself at the moment.

As has been pointed out above, this can be done using the API - you could either write your own plugin to do this, or ask someone else to make one for you. :)