I'm bumping this thread for the benefit of Sonar users who just discovered that development has stopped on their platform.
The backup methods above are helpful for any DAW user—but especially for those who may be migrating to a new DAW.
Nonetheless even if you're only upgrading to the latest version of your current DAW, can it open without a hiccup files created by an earlier version of it—such as the one that existed when Craig wrote this article back in 2003? Probably not.
At the very least, I recommend following his advice about tracking all virtual instruments so that their audio files all start at the same point. That practice rescued my work when I finished a song in 2015 that I began in 2008. One of the VIs from that older session was never updated for Intel Macs, so I couldn't upgrade to a new copy or access it using my Mac Pro. However, importing the audio file of it I created in 2008 was no problem; so I was able to pick up where I left off without much difficulty.