Term limits are an important part of board governance. A term limit helps to provide board renewal and gives an opportunity to improve diversity. However, you do not want all of the board terms to be expiring all at once. When a group first implements term limits, they should set some terms to be longer than others. We call this term limit laddering.
Take a look at your current board members, when do their terms expire? How many of them will be able to stay on for another term and how many will have reached the end of the term limit? Once you do this arithmetic you will know if you are going to have a problem in the future and can take steps to avoid it by adding board members.
Your group should implement term limit laddering to avoid the problem of having all your board members leave the board at the same time.