The best planning in this situation is to petition the court for the appointment of a standby guardian. It can be another grandparent or other responsible person.
This way, when the Guardian passes, the Court would issue Letters of Guardian to the Standby Guardian without a further hearing.
Only a Judge can enter such an order of appointment of standby guardian. The Guardian Ad Litem acts in the best interest of the ward and fails to posses a power of appointment under the legislative scheme.