I found some ancient WRK files that I had used to record some MIDI stuff ages ago. I opened with SONAR, wanting to export the MIDI (and use that in Sibelius as basis for some composition I'm doing).
I selected the MIDI track and clicked Export, but there is no Export to MIDI.
How would one extract the MIDI form a WRK (or CWP) file as a separate MIDI file?

Use File > Save As and set the "Save as type" to one of the MIDI formats

Tnx. Must admit a little confused by the reason to have "Export" and "Save As". The way export works (select tracks and export) made me assume a similar procedure for MIDI. 

You can also drag-drop individual MIDI clips from SONAR to the Windows file system or directly to another application if it supports dropping .MID files.

What scook and Brundlefly are telling you is correct .
Both approaches are useful depending on what your intended use for the midi is .
 
 
Lets say you have a tune that you have been working on , this tune has multiple tracks of midi .
For simplicity , lets say you have 8 tracks of midi going to 8 different soft synths  or even 8 tracks of midi going into The TTS- 1  ...
When you do what scook said  "Use File > Save As and set the "Save as type" to one of the MIDI formats " what you will get is a midi file only that may point to the synths but they are not active or even in the midi project ...
You may see the outputs of the synths in the  track view , I usually delete those and save the file once it is all midi .
It's simple ....once you do it a few times
 
What Brundlefy mentioned is pretty fast and dirty (in a good way )
When you drag a midi file out of SONAR on to your desktop you will have a midi file only of the track you have just dragged ..
I have used that for pulling drum tracks , Piano parts and a variety of different miditracks that I have wanted to work on in isolation ...remember you can always re-import the midi back into SONAR if you so have the desire ...
 
The only thing I haven't done is lasso a group of midi tracks in SONAR and drag them on to my desktop...
Since I haven't tried it I'm not in a position to comment ...I'm sure somebody who has will.
 
all the best ,
 
Kenny 
 

brundlefly
You can also drag-drop individual MIDI clips from SONAR to the Windows file system or directly to another application if it supports dropping .MID files.

that's how I do it.
I do both now. import to browser / just drag+drop
but for the longest time I just used windows explorer (drag+drop)

I save all my projects as MIDI files as a back up plan. Most of the hard work and editing can be your midi tracks..I can always re sing or play a guitar part. 
MIDI files are future proof too. 
 
I use the "save as" and thats it. I can open that file in Cubase as an example. 
 
If the project was all TTS-1 it will play on Media Player pretty close to what you had.