What if the person you're chatting with does not want it archived? (I'm not questioning, but wondering what a protocol would be)
I really want to keep records, so I have a second device, and take a picture of the screen every time I get a message of you.
There is no software or protocol that can entirely eliminate this human problem. The two parties have to have some level of agreement and trust.
This might help with security if it takes as long to crack someone's phone as it takes to expire the messages.
Personally, I want an automatic, encrypted network backup of all my messages so I don't lose them if my device is lost or destroyed. But I know lots of folks around here are excited about the automatic delete thing too. It's going to be very hard to make something that all of us can be happy with.