When we did the party last year, they did not. Monorail service stopped after park hours because the race crosses through Innoventions Plaza. So, the front of the park is basically cut off. ( It honestly was a bit of a mess, honestly.) Even if the Monorail was running, it would be extremely difficult to get back in when the race is on with an
ECV. You would be much better off heading back on a bus from MK to Yacht & Beach Club or Boardwalk - and then entering via International Gateway.