Hi Matias,
I was told by the specialist of the company which sells A/B here in Germany that NiCd Batteries have the least discharge characteristic at 8 Degree Celsius. So he recommended if you want to store NiCd more than half a year to put them 100% charged in a closed plastic sack (to keep the batteries dry) in a fridge.
As for the discharge beyond recovery point of your ProPacs. I found out that if this happens to my Trimpacs, my intelligent 2702 Quad charger won't rejuve those batteries but my solid Twin Fast charger without display does after a while. I usually put the batteries on and off the charger several time, have them around 2-3 minutes on the charger with the lights flashing red-green, then take them off and immediately on again. After a while the red light flashes and the charger starts to charge the batteries again.
Good luck.
Jens