If you get a copy of the Database from them as KAMPFER says you Can carry on on your local machine with the same progress including buildings that you got to when they closed the server.

My original world started out on G-Portal but when it became just the wife & playing it I downloaded the db and when we play that world I host for the pair of us on my local machine. It was easier for me as I was paying the G-Portal account.

Loosing progress for one reason or another is a big gripe on Valheim. Your characters progress you always keep. But the effort of locating and developing a nice base is a big draw to many so really ought to have some building copy facility in game I recon, but alas not as yet.

SO get that db off your mate before they close the server and carry on!