I think we will agree that it is very likely that the sun will rise on 30th. March. It is improbable that the powers of darkness are that effective.The sun will still rise the morning after Brexit.
There will be a few daft stories, some which might be entertaining, but nothing much will happen.
Other than a few Remain zealots looking rather stupid.
It will remain to be seen who will be discommoded. But police on both sides of the channel, will have difficulty if the insurance certificates on goods, lorries, etc are not in order, and unless there are agreements in place, they will be. UK planes will be allowed to land on EU Territory, but won't have permission to take off again. Likewise with EU planes landing in UK Airports. The legal infrastructure has not been set up. So there must be a deal,even if that is a deal for a week, a month or longer, there must be as deal or else commerce between UK and EU stops dead,and only smuggling exists.
The good news is that we DO have a deal. Signed today between the only persons legally entitled to agree a deal.. the European Council and the PM of the UK. In other words a document signed by effectively 28 prime ministers. The deal has yet to be ratified.The 27 National Governments have accepted it, and now two parties still remain to ratify it.
1. The European Parliament
2. The UK Parliament.
The EU Parliament is very likely to vote yes.
The UK Parliament may very well vote No.
In that case, a (new) PM would have to come and publicly unsign it. But at the moment there is a deal.