MrQeu - As PhilE says, the presence of the player who commits the act of foul play cannot be an influence on determining whether, if not for the foul play, a try would probably have been scored.
If his presence is taken into account then you are effectively saying - well he did commit foul play, but if he had not done so he could have still prevented the try.
The point is he chose to commit the foul play - he chose not to act lawfully and by doing so the try was prevented.
To say that if he had acted lawfully he could still have influenced the try is not viable, he didn't, his act prevented the try, so he must be taken out of the equation - in the sense that we must assume, that, since he did not actually do anything legal - then nothing he could legally have done would have affected the try... in other words he is removed from the thought process.