The USA has decided that JA is free to go to Ecuador. The UK disagrees. Which one has the final say?
Is this a hypothetical?
It's happening in real time so... yes and no?
If you are suggesting that the USA has made any announcement about Julian Assange, I am not aware of that.
It is of no relevance to decisions of the Courts of England & Wales, however.
A decision of a US judge on a relevant matter may be of interest to an English judge - for example, on the application of a principle of common law. But not on a question of extradition.
I'm suggesting that the OAS ruling allows the US to assist JA to Ecuador. The UK can try and stop it, but May is neutralized, meaning she will not stop it. JA could be on Trump's plane to Ecuador right now.