It will come as no surprise to you, I guess, that this has never been a question for those directly involved (investors, contractors, and public authorities) : the cost will definitely bounced back to the tax payer.
Besides, anyone who has a little maths can tell the higher of the two costs : a 30y Treasury bond issue or a 30 year bank loan extended to a project company but repaid out of government funds.
The key driver behind PPPs is that governments did not want to raise debt on their own name. Public accountancy window dressing, that's mostly what it's all about.

When through hell, just keep going. W. Churchill