The digital package would be encrypted with your own public key, to which the privkey would be held by you and your fallback recipients (again, could make it 'n of n' to unlock if necessary so no single recipient could unlock it) The encrypted digital package would be useless without the privkey which would be useless without the digital package to decrypt. An attacker would have to compromise multiple email accounts without knowing which email addresses are in the recipient group and gain access to the required privkey(s).