If you didn't take the cave letter with you and presented it to Marcus first BEFORE showing him the sewer letter = yes, quest is broken.
I guess, you addressed Robin too early - but he should reappear again after a while. Even if the quest sequence is broken, you still get XP and (hopefully) the skill from Marcus.

Boratus key: He drops it when he's dead - did you release the wolves, let them have a go at him first and then join into the attack?

Raze has a key download fix for you

Grail cave: there is an exit. I did it like this: placed a pyramid in front of the entrance, went in there, killed Greyface, drag&dropped the grail into my inventory - teleported myself out. Returned later and killed them.
Kiya