If a subbie has closed business- allow an inactive button, which allows you to see their previous involvement without deleting them.
If a sub-contractor has stopped tendering, an inactive button will allow you to see what they've priced without deleting them permanently.
Really good idea! We are committed to improving the functionality of the Address Book and we will continue to investigate and work out the best ways to do it. This is something we will definitely dive deeper into. For the moment as a work around, I would recommend you remove their email address’ (preventing them from displaying at the invitation step), or adding them to an insolvent / out of business list as a way of keeping on top of them.