What are the implications of the whole class failing an exam?
Your question is about the consequences for the lecturer, but you've asked in comments what you should do.

In the UK, if it's felt that noone has reached the required standard then noone will pass. The basic paradigm is that everyone is measure against a standard, unlike in North America where it's more about measuring students against the others in the class. Still, it would not be a popular move to fail a whole class. What the effect on the lecturer would be will depend on their position, and what the uni is like.

Given it's two days from the exam, and I'm guessing it's in maths or similar, I think you should start memorising. The pass mark is 40% (usually), and with high homework scores you can pass with slightly less than that. You're more likely to convince someone you deserve to pass if you can show you've understood the basic ideas of the topic. Make sure you can reproduce the key definitions and theorems, and have at least an intuitive understanding on the methods of proof appropriate to what you are doing.