After an election, councillors remain councillors even if not re-elected for a short period after the election date and this year, because of the coronation bank holiday, the date when everyone changed over was 9th May. The combination of a temporary clerk as you've described and pretty much every council in the country changing probably means a few didn't lose access to their emails instantly to be honest. However, why were important documents being held in the email account of a councillor? Surely they should have been within the files etc. of your clerk (temporary, newly appointed or otherwise) as they would belong to the council not any individual councillor? Frankly rather poor document management if the only copy of a document is held by an individual councillor and no, there's probably nothing you can do if those documents are now lost unless your IT system administrators, if there is one, can recover them.