Don't take this as an authoritative answer, but I think, because you've reached Platinum, your lifetime points will NOT expire. I remember reading that if you're just a plain ole' Gold member, your points will expire after 12 months of inactivity. (Inactivity being no stay, no redemption, no bonus posting, etc.) But since you've managed to move up to the next level (be it Platinum and/or Diamond), your points will never expire.

Not sure if I know of any hotel chains that have initiated any 1 Million Point program like the airlines.

Hope this helps!
Jamester