Also, is this the spot where we split the party?
I should probably just be straight about it: If you ALL stay and fight the monsters, you won't get the staff in time. If you all go for the staff, you'll probably all die before you pull it off.
The general idea is that this finale is supposed to be task-oriented. Someone's got to use the Idols to shut off some pretty potent wards that will kill you otherwise. Someone ought to hold off the monsters so it can be done. Finally, someone ought to try to get down the rift and get their hands on the staff.