Reconnecting contact names with their email addresses

I sorted a list of contacts without their email addresses.
Is it possible to upload the list to Keap and reassociate the name with an email address?

Not really. Email or contactId are the key items to match data.

My recommendation would be to do an export from Keap of the contactId and first/last. Use spreadsheet formulas to match them up, then do a Data Cleanup to upload and match contactIds.