I looked into the BMO Gold Air Miles mastercard, and I went ahead and gave their customer service a call for you. According to the rep I spoke to, what happens is that when you accumulate purchasing levels, points are transferred to an airmiles account. If you do not have an existing airmiles account, one is created for you. She said you can contact airmiles in regards XXXXX XXXXX potential expiration, but she said she has never heard of there being any sort of expiration associated with air miles. From the BMO website there are no references to expirations, and the legal documentation only appears to reference transfers of 1 point per $15 spent, and no awards of fractions of points.
I looked through numerous FAQs and the brochure, and there were no references to expiration. Given the BMO Gold card does not appear to "store" points themselves, I don't believe you have any reason to be concerned.
Now I did look at the BMO customer service forums and saw a reference to points expiring that was posted by a MODERATOR, but it would only be for inactivity (no points activity whatsoever) for 24 consecutive months. As long as you collect 1 point every 2 years you would be OK.
Hi Cestmoi2000! Your AIR MILES reward miles will not expire if you continue to show your Card and collect reward miles from our Sponsors. Only Collector Accounts which have not collected, redeemed, donated or transferred at least one AIR MILES reward mile for 24 consecutive months will become inactive. If you would like to view more information concerning this, please click on the following link which will direct you to the page on our Web site:https://www.airmiles.ca/arrow/Splash?splashId=11500082
I hope that gives you some peace of mind.