When Belkar dies, what will become of his soul?

[hamishspence]

Growth is an aspect of life. No more life, no more growth.

Undead are capable of growing in power, at least (Xykon points out that he's gained XP from adventuring in Serini's dungeon). So what The Giant says doesn't apply to the Not Alive, but specifically to people in one of the 17 Afterlifes - not to those who have "no more life" for other reasons than being in one of those afterlives.

Since Eugene is "on the cloud outside the afterlives" a case could be made that there's room for some degree of change - perhaps he's gotten more bitter, more ruthless.