Complaint was filed and spouse served, but confirmation post card was never returned. Digital confirmation via USPS website shows delivery but there is no signature. Is this enough to confirm service?
Ask your post office if you can get a scanned copy of the 3849 she signed, IF the attorneys agree that would prove her signature. How long ago was it? The green Proof Of Service card has to go through the same processing as all outgoing mail. Then will show up in your mailbox.
In our practice, if the green card does not return, we print out the delivery confirmation from the USPS website and attach that to the affidavit of service. I have never had any issue with this being accepted to prove service.