Head gasket replacement and / or cylinder head replacement?

What is your question?

The head gasket on our 2001 Subaru Legacy wagon has been leaking for aprox. 1 year. How likely is it that the cylinder head has been damaged - needs to be replaced? I've been told the condition of the head can not be determined until the replacement is underway, is this true? Many Thanks.

What makes this problem better or worse?

Hesitates - rough idles sometimes when cold.

How long has your 2001 Subaru Legacy had this problem?

aprox. 8 months