Even as someone who has gone on record as being very critical of the project, it's constant slippages and at a local level leaving the GCR hanging for months in the expectation that a unit could show up at any point, I still think we'll eventually see at least one small batch make it into service.
Why? To save face. I honestly think Porterbrook and the TOCs, Northern in particular, would rather ride out an extended delay and eventually be able to give a fanfare reveal of quote-unquote "new trains" to passengers than lose face, admit that they all cocked up and abandon the project.
If the media get wind of the delays though, it could already prove a PR disaster for all parties as it stands. I think it's remarkable that no paper, even a local one, has yet picked up through the industry that these trains are already half a year late at a time when the network is reeling from the mess made with the last timetable change, and still yet to even turn a wheel in testing.
As an arbitrary guess, I'd expect the first batch to limp into service around Summer 2019, but I'm already at the point that I wouldn't stand by that guess. I just expect the corporate face-saving need to get any sort of tangible outcome and potential good PR to rule over the logical approach, which in this case would be to cut their losses and try something else.