As a one - off CoE would have been fine. As an end to Torchwood as a series it could scrape by but as a part of a continuing show which one would assume they wanted another series of. Can't really see it.

You can have characters changed by developments. You don't have to have Star Trek TNG where people end the episode in the same place they started it but there's a difference between changed by developments and totally gutting the show of anything that drew people to it ie CoE and end of Blake's 7.