I think the rules are very clear that it's the responsibility of the re-entering driver to re-enter safely.

That said, deliberately making it difficult for them to re-enter (especially when it was you that punted them off the track in the first place) is at best unsporting.

I could be wrong about this, but I watched a few times and couldn't see a second contact. It was definitely close, but it looked like Hamilton took evasive action when he realized Nico was hugging the white line to prevent him re-entering the track and then rejoined behind him without any contact.