Can I re-invite a deleted user back to my team?

Deleted users can be invited back to the your team at any time.

Users can be deleted from your Stormboard team if they are no longer with your company, when you no longer want them to have access to any of your team Storms, or if you simply need the license they are occupying. Deleted users can be invited back to the team as a Guest or a Member at any time. 

However, if you simply want the Member to have a Viewer role in your Storms, you can convert the Member to a Guest.