1.) Should be a non-issue - all current versions will remain available for at least 5 versions to come, so in 2017 you should still be able to install and use CS6 in the cloud. The rest is not really relevant - whether or not the file formats will be compatible is only something the engineers can work on on a version-by-version basis and gauging how much effort it will take to maintain legacy compatibility beyond going one version back. Still, if you have access to the older versions, tip-toeing your way up to the latest version and re-saving updated files would be possible. The points in 2.) have been raised a couple of times and I'm sure Adobe will provide some form of offline install, possibly via the Enterprise Deployment channels/ Developer Center, but there's no definitive info yet.
Mylenium