It would be interesting if lennox lewis came back and had a sanctioned pro fight though... he would be the lineal champ and furys and vlads claims at ever being lineal would vanish.... but he wont so it dosent matter.
But then who did Lewis win the lineal title from? Razor Ruddock, Tommy Morrison, Vitali, Holyfield?
Shannon Briggs.
Going by the OP's original argument wouldn't the lineal title have ended with Marciano?
Marciano died, so he relinquised it then. Tyson was the undisputed champion and then he beat the Lineal Champion Michael Spinks. Lewis follows that lineage, Fury does not.