Truly I don't know what happens when a client can't authenticate. My educated guess would be that it just hangs out there until expiration. I have no opinion as to whether Intuit would refund for the expired request.

From an e-filing / Lacerte perspective, sending the e-signature request doesn't change anything about the e-file process. So if a client has issues, you can always mail / fax / securely transmit a PDF the 8879 for them to paper sign and return. Converting the return to paper would be a last resort possibility.

Even my least-savvy clients reported no difficulty with the e-signature requirement, whether there were emails to multiple addresses or just to one.