i think you may be referring to different programs. The Priority Privelege program referred to here was a purchased discount program where, for a fee, you could access discount accommodation and meal rates and was run by a thrid party company. The new Dining rewards replaces that scheme with a similar one (also for a fee) that is run by IHG themselves.
IHG Rewards Club is the free "frequent traveller" type membership which rewards "stays" with points (and other little niceties like free internet connectivity), which can be redeemed for accommodation and also goes towards status tier recognition. That scheme replaced the older Priority Club. I believe IHG points do not expire, but I cannot recall how old that policy is.
To further confuse, IHG have another paid membership which is the Ambassador program which offers different (better, IMHO) rewards but only with Intercontinental.
Hope that helps.