Bit tricky that one. I think common sense would suggest try to call ATC to check if they want you to continue on the heading or to hold at the clearance limit, but then if you can't get in on the RT... Personally, if I've put you on a heading, I want you to stay on it until told otherwise, and if that means you go sailing past the hold it's mostly my fault for forgetting to tell you otherwise.
Sorry if that's a bit vague.