I don’t know where you’re getting this idea from, but Assange is in no way required to flee the UK to accept a presidential pardon for US federal crimes. He would just need to convey that he would accept it through his lawyer, and then he would be immediately pardoned for all US federal crimes.
It’s true that Assange could still be held on any criminal charges he might have in the UK, but these pale in severity to those he faces in the US.
I don’t know where you’re getting this idea from, but Assange is in no way required to flee the UK to accept a presidential pardon for US federal crimes. He would just need to convey that he would accept it through his lawyer, and then he would be immediately pardoned for all US federal crimes.
It’s true that Assange could still be held on any criminal charges he might have in the UK, but these pale in severity to those he faces in the US.