Those patch notes do not say anything about the Spirit of the Oak no longer sacrificing its life to replenish its master's HP when they drop to 20%. I know if it still did this you would loose your Pdef you get for having the pet out, but when soloing, that extra life, so to speak, is all you need to finish off that last add. To no longer have that sacrifice, to me must have been a bug caused by the change to how the pets now buff while out, so needs to be looked into.