MyBB Community Forums

I just had a d*ckwit user on my forum deleting his/her posts for no apparent reason, ban followed ofcourse as this also took away several threads.

Is there a way to remove the ability for users to edit their own posts (or after a set amount of time) and remove their ability to delete their posts ?

Yes, in Admin CP > Users & Groups > Groups > (your selected usergroup) > Forums and Posts and under "Editing/Deleting Options" uncheck any of the following options you don't want:

Can edit own posts?
Can delete own posts?
Can delete own threads?

You banned someone for deleting their own posts, which you had allowed them to do in their permissions?

Weird.