For whatever the worth, I cannot recall ever seeing where audio that had been closed/written to hard drive was lost due to a Sonar crash.
1) Do you get a message about missing audio?
2) Are there any placeholder clips in the tracks?
3) Could they be down in take lanes?
4) Were they present prior to crash, and had they played back after their initial recording?
ANYTIME I finish recording an audio clip, or do any setup task or significant edits, I ALWAYS save the project. I never have to go back as a result. I only offer this as a suggestion for you moving forward.
(additionally, for any existing projects, prior to working on one, I will always save off a copy to another folder, with the Copy All Audio checked, and the location is always to a physically different drive, just in case the drive fails).
VERY sorry for the aggravation - hopefully the audio is just hiding on you somewhere.
Bob Bone