To me Ollanious Pious never died even as his flesh was disintegrated by Horus, from that point on he wasn't a man anymore, but an idea. The idea the even normal dude can influence the history of mankind, especially in the GrimDarkness of the far future. Isn't that what the Imperial Guard is all about? This man is probably more important than most if not all the loyalist Primarchs. Why is that? Because his bravery made him the Patron Saint of the Imperial Guard, the biggest military force in the 40k universe, the actual hammer and shield of humanity against the enemies within and without, you know, the guys that do the lion's share of all the fighting.