The simple answer is yes. If you had saved each of your projects as a .cwb file after having bounced or frozen all your synths and fx you would have had something to go back to. You would still have to have the samples used by programs like Kontakt in the same place as they were in when you recorded the project. Although you could have replaced them if located else where.
I'd suggest you do the following for the future as well as back up your, project to another drive.
If you set Sonar to save Per Project Audio folders then you have a contained location for each project.
You can then just back up that folder for each project.
Sonar lets you select the location for projects, by default this is C:\Cakewalk Projects.
If you were to create a Sonar project in whichever version and call the project My Song.
Sonar would save the project to a My Song.cwp file and place it into the C:\cakewalk Projects\My Song folder along with an Audio folder which contains all the .wav files for My Song.cwp.
C:\Cakewalk Projects
C:\Cakewalk Projects\My Song
C:\Cakewalk Projects\My Song\My Song.cwp
C:\Cakewalk Projects\My Song\Audio
C:\Cakewalk Projects\My Song\Audio\my song 01.wav
C:\Cakewalk Projects\My Song\Audio\my song 02.wav
The outlined method allows you to just backup your whole Cakewalk Projects folder to some external source as you like. It also makes it easy to select a single project to back up as well.
.cwb files can be handy but are also more prone to corruption so are not recommended for archiving. You get the same degree of compression by using win zip or other such program if you need to collect everything together for each project in one zip file.