The German families were forced out and the area was ethnically cleansed and turned over to the Poles including
property, land and possessions. Families were deported and were able to take what they could carry, i.e. not much. Many church records were destroyed or went missing (stolen, sold, buried, ??)
It is one of the lesser known impacts of WWII. Many of the Germans were lutheran or evangelical lutheran. For those of us with families from the area who left prior to the wars, there is little chance (but not totally impossible) of finding cousins.
Now, not all of the church records were destroyed so you need to look (the Mormons are a good source). You would need to be more specific on the town and region you are researching. Some church records are stored in various archives or are still local. Civil records were kept starting in 1874 and many survived and are still available either in Polish archives or through the Mormons and thus, you may be able to trace cousins in this way too.
In short, your research path will be more difficult and possibly non-existent but you wont know until you look for the available records for the specific area you are researching.