Originally Posted by East_and_West

It depends on what kind of miles you bought:

• If they were Tier miles (the ones that count towards your membership level), they are valid for a year; they will thus expire on Nov 6 this year, unless in the meanwhile you get upgraded to the next tier (Silver/Gold), at which point the count starts over from zero. There is nothing you can do to keep Tier miles from expiring.
• If those you bought were Award miles (the ones that you can use to get tickets), they do not expire as long as your M&B account remains active.

At some point I remember reading somewhere in this forum that you need to register with M&B a paid flight on A3, OA, or any *A member at least once every 5 years to keep your account active. A couple of months ago though that I skimmed through T&C on behalf of my brother who has an virtually inactive M&B I could not find the relevant entry, so it is possible that even this requirement may have been removed.

Originally Posted by irishguy28

Stay alive.

It really is that simple.