Hello, scp and rsync with ssh (as far as i know) , both use the ssh service for communication, this means it is necessary to have such daemon running. But here my question, have you ever seen an ssh service crashing? O.K. there were reasons that the target computer is not answering (hard disks full, whole computer hangs), but in this case it makes no sense to have ssh running and the rest is blocked. I have never seen a working machine where only ssh daemon was hanging, in most cases a lot of other things were not working correctly but on ssh the machine was reachable and managable.
By the way: rsync is a mighty tool it should fulfill all your requirements....
Regards Randolf Balasus