This is something that somebody should have said to the OP at the start, way before the abuse that he managed to get for asking a simple question, something which actually hasn't be covered here.
The basic answer is: Dobbie can technically play in the semi-final against Brighton, he just won't.
I think the OPs point is the fact that it is a gentleman's agreement. It isn't written into the loan contract (said so by CPFC). Thus they could go back on this and let Dobbie play, it is unlikely, but they can. That as far as I know is something that hasn't been covered on here at all.