Looks like Boris has been found out and isn't going to con parliament into agreeing to an October election so that he can then change it to November and force through a no deal Brexit. So assuming the EU agree we're probably looking at a Jan 2020 extension and an election in November /December.
Having stuck his neck out for an October Brexit Boris will increasingly looking like what he is - a loud mouthed public school pratt - and what credibility he has will be seriously dented. If he can't do a deal with the Brexit Party the Tory vote is going to get split (as per this poll) - which will result in Labour and the Lib Dems nicking seats in the Midlands and the North. Remain voting Tories will flock to the Lib Dems in the South East and the Tories will get decimated in Scotland having lost (the very popular) Ruth Daley.
There will be no party with an overall majority and the Lib Dems will decide whether to join the Tories or Labour in a coalition government. There's no way they will form a government with a Boris led Tory party but might go for a coalition with Labour - especially if Corbyn steps aside. A Labour/Lib Dem coalition will call for a second referendum which will result in a vote to remain on the basis that many people have realised the mess Brexit will cause, a good number of the nostalgic older generation who voted leave originally will have popped their clogs and yet more younger remain voters will be on the electoral register.
There will be riots in the north and the Midlands and in rise in the popularity and profile of the far right. The Tories will refuse to condemn the riots and in horror yet more centre ground Tories will defect to the Lib Dems. A right wing Tory rump will merge with the Brexit party to form the "acceptable" face of the right and effectively condemn themselves to sitting in opposition for a generation. The arseholes behind the far right parties will be rounded up and jailed and the riots will fizzle out.
An era of peaceful economically sane government will ensure with the UK part of a liberal, Social Democratic Europe.