Quite often, I don't archive the midi and synth..... I delete them when the audio sounds like I want. Yeah I know.... I can't go back and edit something..... but that's the way I work. Sometimes I kick myself but mostly, I like the result before I hit delete and never look back.
I used to do that, too. But too often I'd later want to edit a MIDI part or replace a soft synth with something better that I'd acquired since the project was recorded, and be forced to re-record the part.
Nowadays I put the original MIDI/audio synth pairs into a folder, archive and hide them. That way they're as good as gone as far as SONAR is concerned, but can still be retrieved in a pinch.