If you have a Level 100 Hardcore character you should try keeping it alive because dead characters won’t carry over any Altar / Map (fog of war) credit when Season 1 launches on July 20.
Let’s say you have a Level 100 char who has collected everything and cleared the whole map. The char dies and you stop playing until Season 1. Since you cannot log into the character that has everything, no credit will carry over to your Hardcore Seasonal character.
This was also confirmed by Associate Game Director on Diablo 4 Joe Piepiora on Twitter.