As humble cc... in the company I work for we are trained that in the event of single pilot incapacitation the remaining pilot might want us in the empty seat to read check lists. The emphasis is on 'might' as in that unenviable position its up to the remaining flight crew to decide the best course of action. I certainly wouldn't question a captain's/ FO's decision to put a call out for say " an ID80/90 pax with ATPL" if he/she felt that this was the best option.
And addressing the query on decompression - after the Helios tragedy the cc drill has now changed so if the descent does not commence (after a specified period) then cc report to the flight deck to investigate.