Please give a little more information so we can help. Specifically......what type of points are you referring to with Marriott? Marriott Rewards Points (there is no expiration) earned on hotel stays, Marriott Visa card purchases, etc. or are you referring to Destinations Points (The Marriott Vacation Club program where points expire after two (2) years.
Voyaviajar, if you are referring to Marriott Rewards points, then you don't really have to worry about them expiring. There is a section in the MR terms & conditions that states:
A Membership Account may be closed at the Company's discretion if no Points or Miles are accrued during a 24-month period. All Points in the Membership Account will be forfeited at that time.
However, this is a very rare occurence, and usually requires some extenuating circumstances.