That’s not necessarily accurate. Article 50 says that a member state can leave in accordance with its own constitutional arrangements. There is much scope for argument that a country cannot be taken unlawfully (in terms of its own constitutional arrangements) out of the EU. The principle that you can’t benefit from your own wrongful act is of course one that is recognised in our own law as well as in other legal systems. The law of the UK is that Boris is compelled to seek an extension in the circumstances envisaged in the Act, and as Lord Sumption said last night there doesn’t seem to be any wiggle room in the Act. If he unlawfully fails to comply, the principle that a member can leave in accordance with its own constitutional arrangements might be offended.
It is of course ultimately a matter on which the ECJ would have to pronounce, if it actually arose, and there are as always arguments both ways. But I think there is a respectable argument to the effect that an act of Martyrdom by Boris by simply refusing to comply with the law would not lead to us crashing out without a deal in any event.