I doubt Gon or killua will be apart of these next two major arcs - at least he won't join the dark continent.
1. He has no reason to join in at the moment and even then if something were to happen to kurapika,his dad or leorio no word would get back to Gon for months if ever
2. He has no drive to return to hunter association atm he didn't just give up his nen to get revenge on Pitou he gave up his innocence and much more which he is reflecting on in himself and chose to life a simple life with his aunt.
3. There is not a single soul left to teach Gon how to regain his nen atm. It'll come much later, maybe killua can make a wish for it but it'll be more complex and need to be actually fleshed out.
1. He has no reason to join in at the moment and even then if something were to happen to kurapika,his dad or leorio no word would get back to Gon for months if ever
2. He has no drive to return to hunter association atm he didn't just give up his nen to get revenge on Pitou he gave up his innocence and much more which he is reflecting on in himself and chose to life a simple life with his aunt.
3. There is not a single soul left to teach Gon how to regain his nen atm. It'll come much later, maybe killua can make a wish for it but it'll be more complex and need to be actually fleshed out.