i'm in the head gasket camp as well.
as has been said, don't drive it. that will cause a groove to be formed on both the block and head surface, [if it hasn't happened already, driving it the 20 miles you stated] requiring the engine to come out to get the deck milled.
that may have ruined the block if the groove is way deep, or may cause you to use head gasket spacers if they are available for that engine.