Im currently using laravel echo for my realtime chat app using presence channel and facing the same problem with this question.
Different thing is that I'm using Laravel echo server instead of pusher for socket server.
However I'm looking for laravel echo server side implementation beside pusher webhooks to get notified of user disconnects.
Any possible solution?
Answer to my question. I found a PR on laravel-echo-server which has hooks feature to listen to client-side events from server. Finally I'm now in peace.