We can't really rule anything out, and that's part of the problem. No one has a clue what's going, including and especially the people making the decisions.
A serious question that has to be asked is how quickly can we 'recover' from a No Deal situation i.e. revert to pre-existing customs procedures?
As quickly as you can hold a second referendum.
(Unless the No Deal is bad enough that a cross-party consensus emerges for rejoining CU/SM - i.e. Norway - but I'm not sure we should wish for that to happen.)
There is not going to be a second referendum in the near future. Neither the Tories nor Labor under Corbyn have interest to do so. The Tories are too divided and the Brexit hardliners would break up the govt. Maybe Labor would support one, if a Blair-style leader was still around.