I have to say that majoritively i agree with seven stars (and your case law is up to date).
With regards to D.R.E and lesbionic, you are both wrong and both right in some ways.
A GBH charge will not be applicable here but any of the following could be:
1) Murder - in the Cheshire case – court of appeal shifted the point of focus away from the question whether the original wound was still an operating cause at the time of death to whether death was attributable to the acts of the accused. The severe loss of blood due to the stabbing and the leaving the door open could be attributable to the death of B. The final blow to the head made by C, although was the final cause of death, may not have been fatal had it not been for the loss of blood, allowing the arguement for murder to take place.
2) Attempted murder or mansluaghter. If it is found that regardless of the loss of blood, B's blow to the head was the only cause, dependant upon the mens rea of the accused (A) would depend whether an ettmepted murder or manslaughter charge was appropriate.
With regard to D.R.E's 'factual liability' he is correct in saying it must be establish. Both factual and legal liability are to be satisfied. However, the factual casuation is a but for test.
But for A's actions would B have died? there are arguements for both, my advise to the OP is to argue both yes and No. conclude with what you think the outcome might be, but tehre is not need to make a final decision, just show that you know the law and can argue it well.
to D.R.E and Lesbionic - i dont mean to be rude or patronising here but i see no need to come to a final conclusion. Such cases as these are decided by juries, although upon the guidance of a judge. It is not a law students aim to make a final decision that we are not equipped to make. could and perhaps are the words you should use, not definitives else you cut yourself short.
You failed in advising the OP becasue you became too obssessed with your own ego to appreciate the arguements you both presented.