Foggy and Marci might have Marci's canon role at the end (ie: steal legal documents with info even Matt can't get. Or maybe hard proof of things Matt knows but has no way to prove), but remain all in all pretty secondary.
They might also, maybe, get in league with Karen at some point. The question here is: would they?
Maybe yes, if Fisk did something they couldn't pretend not to see. Like, Marci stopped joking when señora Cardenas was killed. I think finding out the bombings were Fisk's doing was also part of it.
We probably won't have Fisk doing any of those. But maybe something else, equally big/murdery?

Or they could be evil, but help xD
Having Matt and Foggy be not-friends hurts my heart (*ignores what she had happening to Matt on the very first fill*)

(But yes, maybe they'll go with Nelson&Stahl at the end. En masse freeing of slaves will require legal work!)