The world is filled with "Ifs". But what we know is that we've likely just lost a much needed new nuclear reactor because of our withdrawal from the EU. If a new and cheaper and better nuclear power station appears in its place, then it will be a good thing. But you can't argue the loss of something good isn't bad because hypothetically something better might happen. Are there fallback plans for Hinkley that mean we'll put in a better reactor? No there are not. There's just no new reactor. As a DIRECT consequence of leaving the EU.
I mean I could respond to almost any bad thing by saying "but if the government came in and fixed it in a better way, it wouldn't be bad." But as a meaningful response it wouldn't carry any weight unless it seemed like the government was going to do so. You seem very pro-Brexit but the loss of a nuclear reactor with no alternative in consideration cannot be spun as anything other than a loss.
But no doubt we'll make it up with windfarms. :/