In the Wisconsin State Journal, this question and answer was given:
Question: What happens if the recount isn't completed by then?
Answer: If the recount is certified by Dec. 13, the state's results are guaranteed under federal law to direct which candidate electors vote for on Dec. 19. After Dec. 13, Congress could vote to choose which candidate gets Wisconsin's votes, with the governor breaking any tie between the House and Senate.
I think the Congress will let Wisconsin's original 10 electoral votes stand.