Everyone here is missing the boat.
In all likelihood, Congress will not be able to override the veto even if support remains behind the bill. The bill has not been delivered yet to Trump, and once it gets to him, Trump can pocket veto the bill for 10 days before it would take effect, but by then, this congress would be dissolved and the entire process would have to restart.
In short, the president can ignore the bill. Generally, a bill that is ignored will automatically become law after 10 days. In this case, however, 10 days would be after January 3, and this congress -along with any unsigned bills - would be terminated. In order for congress to vote on a veto override, the president would first have to veto it. He won't veto outright, as the timing is prime for a successful pocket veto.