If you are not in regular contact with a family member or friend there is no definitive way to find out if someone has passed away.
If you are not named in the will the executor of the estate is under no legal obligation to notify you of a person’s death.
When it comes to time limits passing people often say 'but nobody told me!' The truth is, no one is obliged to tell you. You find out if someone passes away by keeping in touch with them and people around them and checking obituaries regularly.
Another method is to contact the Supreme Court Probate Division in each state and ask if an application for a grant of probate has been made on behalf of that person.