Barnier, in the Youtube link I added above, clearly says there will be no hard border in Ireland whatever the outcome of Brexit negotiations. CHECK
and then... some nice and reasonable words about future cooperation... CHECK
...and then... "leaving the EU means leaving the customs union and single market" - very clear, as he has said repeatedly. CHECK
[I have no idea why Labour keep saying otherwise, and that their plan (which seems to, even though they have never fleshed it out, include certainly the customs union and also perhaps the single market) they've talked to the EU about could/would work.]
...and then... "as President Tusk has said, Britain can still stay in the EU"... &, that seems to be what the House of Commons are working for.
The leaving with no deal scenario on Friday means no hard border in Ireland, no inclusion in the single market, no inclusion in the customs union, but continued close partnership with the EU, and a start to working out a trade deal. The EU has already put extensive plans in place to help a smooth transition during this scenario.
Brexit preparedness: EU completes preparations for possible “no-deal” scenario on 12
http://europa.eu/rapid/press-release_IP-19-1813_en.htm
^ extensive details here.
There is no reason not to leave; the problem is with the House of Commons.