I take first the potentially wrong assumption that "quit" is not meant literally.
To the question of (ethics) violations by the instructor ...
A faculty member may have to file written forms before he/she goes away from teaching duties for a situation known in advance. The forms should document what is to be done in the course(s) that will be missed. They should be signed off by the department and perhaps all the way up through the college level before the trip is taken.
--> Ask your SGA representative and/or the Student Affairs Office to establish what protocols are required of faculty who will be absent from teaching duties. When forms are to have been filed, the director's claim of ignorance means either that he/she is lying or that the faculty member failed to follow protocols. One or the other deserves an administrative rebuke. Otherwise, when no official policy is in place for this case, your student organization needs to fight to establish one.
--> The next step is to file a strongly worded statement with your representative student organization and/or through your student evaluations. Regardless of whether an official form was or was not to have been filed before the trip, the instructor of record bears full responsibility in this case to assure that his/her teaching duties are properly handled in his/her absence, especially when the absence was planned in advance. The department chair, the college dean, and the university provost should hear in writing from the entire class about his/her negligence to fulfill this responsibility.
You may instead mean "quit" literally, as in "The instructor pretended to be going to a conference but actually was resigning without telling us the truth".
--> This case is entirely out of your hands. The administration above, starting the the director and finishing at the provost, have to handle the violations.
Preparation for Exams
The director is telling you to do something different than what you expected would happen. The best you can do is do as requested. I cannot attest to whether the requirement is or is not excessive. To address this, you could determine whether it would have been any different had your instructor been present. Ask students from last year's or last semester's class for insights. I will add however, the director has the responsibility to not leave your class just hanging to learn it on your own. Your class can/should petition for a make up session to cover the material when it is to be required on an exam (the final exam) for the course.
By comparison, your class cannot rightfully petition to have a make up session to cover content on (national and professional preparation) exams that are not part of the course syllabus. You can only request to have a preparation session for such exams at the graces of the department.
Being Set Up for Failure
Is the university (purposely) setting up your class to fail? ... Most assuredly not (on purpose). At worst, the university has set itself up to fail because it does not have a way to assure a responsibility of its faculty to their core mission. This is a longer discussion for a different thread.
Unfortunately what has happened instead is, the instructor of record has set up your class to fail. While Hanlon's razor is invoked, I do not see stupidity at play in his/her case. When the instructor is truly only gone on a conference trip and was to have followed a formal protocol to file forms before the trip, this is a most glaring case of official negligence of duties. Even absent that he/she had official requirements to file forms, the instructor has neglected his/her contractual obligations by not handling the responsibilities for his/her teaching duties completely and with all due attention.
When the instructor just quit and had kept that plan hidden (from everyone), he/she bears the full brunt of the blame--the university is just a bystander to the destruction. Even as a bystander though, they have a responsibility to clean up the mess fairly and equitably.