If you have ever said "who is playing the cleric" then you have asked who is our healer/leader role.
Stalker.
The only take I have on roles is the "away" part.
I'm glad I've never heard this, in all the campaigns I've DMed or played in, no class was ever expected in the party (2 rogues and a monk, fine).
A role by any other name smells as meta.
No where did I use the term "expected", not sure how you have "never" heard of such things.