I quit this site around $15$ months back. Now I am back and I see that my inbox still has my old "achievements", "comments", etc. Is it possible to link back to my old answers and questions?
It is most likely possible to have your old submissions attached to your new account, however this is an action that can only be done by those with access to the database: SE employees. Your best option is to contact the SE team directly with your request, explaining the situation as fully as possible.
I know that deleted accounts have been reconstituted in the past, but those that I am aware of were exceptional circumstances; much more exceptional that your history.
Be aware that in making this request there is no guarantee that SE will accede to it.