He will when (not if) he accepts the extension until January, which he is legally compelled to do once it is offered.
As soon as he does, Corbyn has zero reason to refuse a GE and it happens.
Johnson will wipe the floor with Corbyn in a GE but we'll still get a hung parliament in all likelihood with the Tories as the biggest party.
It then comes down to pure numbers - if Johnson has enough and parliament can't "Benn Act" him in January, we'll leave with a deal or no deal. If he can't, there's only one option left - a second referendum.