No formal expiry date for Superpoints exists.

But:
* the Coop Superpunkte program can be terminated any time = getting new/additional points can be stopped anytime
* the current 'contract' with miles&more is so far only running until the end of calendar year 2011 (and when they did renew that contract last time Coop was in heavy competition with Migros and did only succeed with a last minute effort)
* conversion rates (current one is 2:1) into miles&more can be changed or completly stopped (unlikely) or quantity limited any time without pre-notice.
* promotional conversion rates like the recent 3:2 can be changed or stopped completly (and are only recently now quantity limited anway)