I'm sure that Marriott has some wording somewhere in their T&Cs that would allow them to close an inactive account. But the reality is that I don't think they worry too much. My wife used to travel for her work back in the early 90s. A year or two ago, I signed her up for a Marriott Visa card and remembered that she already had an account. When we checked, the account was still usuable (after more than a decade of inactivity) and still had almost 40K points in it.