There is no formality here.
Such uncharted waters and BoJo can do many things to interfere with things and he could also move a motion of no confidence.
But either way, he doesn't have to abide by the Bill if he doesn't want to and can deal with the ramifications later.
The people will still make their wishes known, and this is where BoJo will gain encouragement from.
He is't running from the people. The Remoaners are and the people see that.
In the end, he is still PM for now. He can do what he wants. In fact, I don't see how he has much choice unless he feels confident he will win a majority for sure. I only rate his chances of that at 50%.
If he wins a majority, then he will overturn EVERYTHING and proceed with NO DEAL anyway. I only give him a 50% chance.
So he only sure bet is to not ask the EU for an extension and crash out and deal with all the legal ramifications. He may need to take one for the team, and that will make him a hero to millions of Brits.