I can give you some tips.
The terminating question that allows you to skip from the MAIN survey to the CBC survey needs the following ...
1/ Place the terminating question at the very point in the MAIN survey when you are ready to skip to the CBC survey.
2/ Tick the Link Settings box and insert the link to the CBC survey with the pass in fields included within the link (panel member ID and panel provider ID). Here is an example of a typical link passing in mypassword=michael and zip=98370 ...
Use the example above as a guide.
3/ Do not tick the Terminate Respondent box as you want the MAIN survey to remain as incomplete (given the respondent will leave the MAIN survey, link to the CBC survey and then jump back to the MAIN survey to finish off).
Include the panel member ID and panel provider ID as pass-in variables in the CBC survey.
When you terminate from the CBC study, it's okay to tick the Terminate Respondent box. Also select Qualified / Complete as this will tag the survey as completed when leaving the CBC survey. You need to insert the link that takes you back to the MAIN study. No need to pass back any ID variables because the MAIN survey already has them captured. You will need to inform this link where to skip back to the MAIN survey though. There is a feature that needs to be included in the link called "sys_skipto". See example below.
This enables you to jump back to the very point you require to continue the MAIN survey. The above example is skip back to Q11 in the MAIN survey..
The terminate question in the MAIN survey will be a simple tick the Terminate Respondent box. Also select the Qualified / Complete option. No need to tick the Link settings box.
I understand you are not using Sawtooth for the MAIN survey but I'm trying to explain how the linking process would normally work for a total Sawtooth project.
From the examples above you should be able to sort out the passing variables via the link okay.
Hope that all helps?