JGR01 hit it right on the head.
If your ever rebooked on another carrier and given a paper ticket then that flight cancels, go and demand your paper ticket back .
Once your eticket has been printed to paper then it can not be changed back to an eticket or reprinted.
I cant remember for sure but usually an agent needs to get a FIM (cant remember what it stands for right now, but it is really a check written out to the carrier , and requires the AA agent to leave their first born child as a security deposit) if the paper ticket is not available.