The original building is still there (calling it a terminal sounds wrong) but it can easily handle a plane load of passengers. I expect just a bit of paint and few new chairs are needed.
Plans have been submitted for a terminal and associated apron to be located next to the new big sheds - it's seems to double as a new headquarters for Stobart Rail (terminal on the ground floor, offices etc on the first floor)
http://publicaccess.carlisle.gov.uk/...17-2111745.pdf