Originally Posted by Unregistered

No they won't, they won't even ask you for your new transcripts when you join. As long as you don't fail and have to retain one more year, just shut up, don't say anything about your grades to the firm, and live your life normally.

The whole point of providing TC in advance is for the firms to "book" your availability. It would reflect really poorly on them to withdraw the offer (and who would sign with a firm that willy-nilly withdraws offers?), so it's never done unless you're involved in academic dishonesty or criminal activity.