Proroguing Parliament is a done deal. So pretty much is no deal being made Illegal. As is the fact rhere will not be a general election before the 31 Oct. the other parties will demand later if and when they agree to it.
So Boris is blocked in. He will fight it for a few days to try to get Corbyn to agree it, he may even try to bring a new bill forward to permit it.
But right now it looks like he either seeks an extension or resigns. He does have other options though.
He may get a deal from the eu that's acceptable to the majority of the house, a customs union for example would likely scrape through the house, allowing us to leave at the end of Oct, and the eu would accept it, so there is an option there and it removes rhe need for a back stop..
Alternatively he could delay and go for a second referendum. Give the people want many of them want.
None of these are likely but they are possible, as he needs to find a way through this.