I think a fair system would be X years after publication. * If you die X+1 years after, your kids get nothing. * If you die the day it's published, your kids

I think a fair system would be X years after publication. * If you die X+1 years after, your kids get nothing. * If you die the day it's published, your kids get X-1 day. * If your kids discover it after your death and publish it, they get the whole X years. Around 40 years seems like a reasonable value for X, in my opinion.