I recently used both the powder and liquid versions of Technidol that I purchased around 1988. The results were just fine, and they were stored in a cupboard in the house.
As David mentions in his post I think the developer would only go away if the yellow gods end of lifed Technical Pan.
If you get the chance try Tech Pan developed for 25 minutes in Rodinal diluted 1:200. You may not want to worry about Technidol going away.