Hello,
Based on your description it's not entirely clear what you have in mind.
The following scenario is not possible without making code changes:
- the respondent will answer several question through the SP survey first
- on answering question nr. x there will be a redirect to an external site ;
- all previous answers through the SP survey will be taken along to the external site to be processed externally;
- etc.....
[possibly return to the SP survey, next continue and submit all answers?]