Maybe you could update the meetup page, asking if anybody wants to volunteer to restart them? I moved here only recently and wouldn't be able to do that for now, but maybe somebody else could.
As it stands now, I suppose that most people would just sign up and wait.
Folks are welcome to start a fresh HN London meetup much like we did when we started. If you are new to organising events starting with something small and manageable would be much easier than trying to pick up an event with 400 attendees.
As it stands now, I suppose that most people would just sign up and wait.