Morgansfort without casters?

Gottri, Thrur and Barziduque - read no further or I'll cut your beards!

I've started running Morgansfort a couple of sessions ago for a group of very experienced players. They are quite careful in threading and have managed to deal with a lot with only one death so far. Problem being - we have a full party of fighters and there is a possibility we won't have any casters by the time they make it to the last chamber of The Olde Island Fortress - which is magically sealed. Nobody to cast "Knock" or read scrolls with it.

What should I do?