Choose one sentence that has the same meaning as the root one:
The whole project would have fallen through without his support and hard work.
Had it not been for his support and hard work, the whole project would have fallen through.
Because of his support and hard work, they had fallen through the whole project.
They had fallen through the whole project, thanks to his support and hard work.
If there had been his support and hard work, they had fallen through the whole project.
Had it not been for his support and hard work, the whole project would have fallen through.