Question:  If the Approver changes, will the email address be updated?  If not, both options would fail.  Can you not do a lookup at the time the form being used is created?  And the lookup used UserProfileServices or some other source you know will be current.  

Thank you for the quick response.

Yes, I will be doing lookups when the form is created, not just for user names or other profiles, but for other fields as well. I might need to look up an external address that cannot be computed by the 'userProfileLookup' function. Is there an advantage or disadvantage of doing this lookup when the form is created as oppose to having the workflow do the lookup doing its run. I am new to Nintex development so I would like to learn some 'best-practices.'

Hopefully a best-practice person will provide some insight here - for myself, if there is no degradation (slowing the opening performance) of doing the lookup when the form opens, I'd rather get the information then (I can verify it loads correctly); the workflow can do other work, as needed, when the form is submitted.   

Thank you, MC. That, too, is my preferred way. As you have stated, I am able verify that the correct value loads correctly.

Thank you for your input.