The deal is...
there are very specific reasons (you can read them in DS230, part II) why you can be denied GC during CP. also read immihelp.com statements.
if it is a documentary requirement then you have several choices:
1) if you can arrange for the document while outside US, they will let you go and ask you to come back with evidence.
2) if you need to come back to the US to get the document, they will let you in - they won\'t cancel your H1.
if case 2) above, i don\'t know if they will let all applicants in or only the primary. maybe only the person required to come back will be allowed, say for example some documents that secondary applicant is missing and there is no need for primary to get back to the US, only secondary comes back.
the exact procedure is not known and so nobody knows when they actually cancel your previous visas i.e. before they make the decision on your GC case or after.