Release from ward of sectioned person without s17 in exceptional circumstances

Can a nurse legally let a patient on section off a ward without s17 in exceptional circumstances?

For example if an ambulance was with a patient for say a cardiac arrest would the nurse have to wait for s17 to be written up to let P and ambulance out go to a and e? This could possibly be a factor between life and death over paperwork!?!
However with the wording of section 128 MHA 1983 - Assisting patients to absent themselves without leave, etc.: ‘Where any person induces or knowingly assists another person who is liable to be detained in a hospital… to absent himself without leave he shall be guilty of an offence’ This dose not appear to offer an excuse of reasonable excuse.

To make it more complicated if the nurse refused to let the patient (with paramedics) out would they be committing an offence under Emergency Workers (Obstruction) Act 2006? If say a patient did die and a coroner said that the if the delay to go to A and E had not existed then the life chances would have been significantly higher; then a good barrister could make a case for negligent manslaughter by the RC or nurse potentially?

It’s a legal black whole can you help me out?

As with my suggestion over wat happens if the police arrest a detained patient on a ward, this is another question were practicality has to trump any potential gap in legal authority. If a detained patient needs emergency treatment and an ambulance crew decides to take that person off the ward for this to happen, then that trumps all other considerations. No health professional should (or would) stand in their way until the right paperwork is in place. Some RCs, if they anticipate a patient may need emergency care, write this scenario into the parameters of authorised leave so the question doesn’t arise. But of course it isn’t possible to anticipate everything and in the event of a medical crisis that comes first. Ward staff should of course let the RC know what is happening as soon as they can, and the RC can authorise leave (including over the telephone - there’s no inflexible procedure for granting leave) even retrospectively if necessary.
I think any concern about s.128 is academic: no-one has ever made that link as far as I know, and in practice it is unthinkable to invoke that bit of the MHA in this situation.
Mat Kinton (CQC National MHA Policy Advisor, personal capacity)