Does a durable Power of Attorney become invalidated after the death of the party that created the POA?

Yes, POA ends upon death, and this can sometimes create a "catch-22" situation. I became POA for an aunt after her previous POA became ill. When aunt died a month later, before I had time to get things in order, I discovered that aunt's will, which named executor, was in her bank safety deposit box. I could not access the box because I was no longer POA. Lawyer had to go to court to get an order naming me "temporary executor" so that I could get the will. I ended up being executor anyway because first person named was the POA who was ill. Lesson learned - keep a copy of the will somewhere other than the safety deposit box.

Yes. POA is not valid upon death.

I have held Power of Attorney for four different loved ones. Each document was created by a different attorney. All four attorneys stressed that the POA becomes invalid with the death of the party that granted their POA. It may not be significant but all the documents were created in Alabama.