I don't think anybody thinks anything is going to happen tomorrow. The danger was before the Withdrawl Agreement was signed and sealed that the UK would leave with no deal. Everything carries on as before until 31.12.20. The UK still pays into the system and has access to single market and customs union. 

The question is what happens on 1.1.2021 Will there be a deal or another extension of the transition period or will the UK leave with no deal? 

The only difference until then is that the UK has no representation, can't veto laws it has to obey until the end of the transition period, and I (as a UK citizen living in France) no longer have the right to vote in the local elections in the town I live in (coming up in May) as you have to be an EU citizen to vote. But that is democracy for you!