Many, or most, airlines and hotel chains advertise that their miles / points ‘never expire,’ but that is only half-true. They may not expire, but they can permanently disappear from your account if you are not careful. This blog post tells what you can do.
In general, you need some sort of activity in your account to protect your miles and points. In a few cases, such as All Nippon Airways, your miles do expire and there is nothing you can do to prevent it…use them or lose them.