I'd never trust any sort of autosave.
It's all too easy for it too kick in when you've just inadvertantly deleted something.
No, it's Ctrl + S all the way here.
As for versioning, that itself opens up a whole rats nest of misinformation & problems.
It's all too easy to fall into the trap of simply doing a "save as" and incrementing your project from e.g. "My Song 1.1" to My Song 1.2"
Then, one day, you decide to clear out your system a bit and you realise that there is no easy way to delete not just the .cwp of whatever song it is you want to clean up, but also all the audio tracks that go with it.
These will all mount up in the project audio folder and you won't have a clue which bit of audio goes with which particular version.
(A workaround is to do a 'save as' but to a totally different part of your filesystem, this ensures that Sonar COPIES all the audio files to the new location, provided you've got that option checked).
Now, you can do what you want with all the other, outdated versions, copy to Backup & delete being my choice.
I freed up 250Gb of disc space over the weekend, just from doing this on 15 or so projects.