Boards get removed after 2 months, regardless of activity. This is because of 2 reasons - 1 it automatically removes old/inactive boards from my db :). And 2 it keeps the boards/tasks more focused for about 4 sprints. I've received a lot of feedback about making the boards stay alive as a paid feature, but I'm not going to make something paid when you can just go to a competitor like Trello if you want persistent boards.
Yeah, I like this instantly shareable and trackable in calendar, but I never found anything more convenient than to maintain a kanban board on a excel sheet and the file placed in a shared folder which the team is having most probably to share stuff around.
About the boards expiring in two months: does that mean two months of inactivity?