There's not a big issue with standard of care... and BWS is not even formal law in Australia... are all of you really doing crim or have done crim?
The standard of care exercised by the paramedic is of minimal importance in this question. His treatment needs to be 'palpably wrong' (R v Jordan), not just 'thoroughly bad' (R v Smith) to sever causation. Bear in mind that the court is going to be VERY RELUCTANT to acquit a killer just because the patient later received some bad treatment.
Even in Evans and Gardiner, the doctor's failure to find a fatal, fractured bone was not enough to sever the accused's causation because it was merely bad treatment. It's not as if he did anything wrong. In this case, all the paramedic did was fail to give him treatment based on his medical expertise. He 'didnt accelerate the victim's death', which appears to be a threshold we need to overcome to sever causation (Evans and Gardiner).
And bear in mind, failing to get treatment is merely a 'loss of opportunity' to live(Bingapore).
So based on all these factors, one would reasonably conclude that the accused's actions were still an 'operating and substantial cause' that 'subsisted' up to the death of the accused (R v Hallet).
On the question of intention, you don't need to have 'desired' that the victim would die or receive GBH as a consequence of your actions to establish intention. It is sufficient that there is 'virtual certainity' that the victim would die or receive GBH. So, for example, if I attach you to a electric wheel chair and press the button, I don't need to desire to kill you to establish intention. In fact, I could be indifferent to whether you die or not. But it is still sufficient to form intention because I had 'virtual certainty' you were going to die. (Woolin, Hancock & Shankland).
Finally, a note regarding provocation. Delay is seen as an important factor by the Privy Council in R v R. It wasn't by the High Court. But later on, one of the judges in High Court conceded that his earlier partake in the majority judgment was wrong. So I guess the only conclusion we can draw from this is that delay doesn't bar provocation. It is a consideration, but not conclusive.