I somehow lost Festus to the mechanic patrols while gathering gold >_> and I can't find any revival person in the Academy.
I seem to recall hearing something about being able to return to Somnus safely via saving in some location or another, but I'm not sure what.
As of TRPG2, there is no one that has the power to revive the dead other than the shadowling queen. Once you leave the Queen's service to join the Psy Academy, you will be unable to revive your allies. Also, you can't explore Somnus once you agreed to the Dean's proposal. Sorry, but you will have to finish the game without Festus.