taking the student sierra image to a mojave provisioning process is a big jump. a lot of the work is predicated upon the applications you are laying down of course.

with mojave you're going to need to deploy everything from kernel extensions, configurations for the transparency consent & control database, might need to update some applications, etc, etc.

If you are stable at 10.12 & have no reason to go to Mojave then I would say stay at 10.12 & create a student beta mojave provisioning process build before making that decision.

I've gone from 10.12 to Mojave without major issues & the end users are very happy.

I'm sure there are other variables in your environment (like if your users are standard or admin accounts), but I would consider security as a reason to make the leap to Mojave. Apple only provides regular security updates for the previous 2 versions of macOS. I can't find the blog post, but when 10.14.1 was released some admins noticed that not all the security fixes released for Mojave were being backported High Sierra and Sierra, implying that latest release of macOS is Apple's focus in terms of keeping everything patched.

I totally get your position, though. If Macs are being completely phased out, why change your deployment and setup process? If you know all Macs will be gone within a year, maybe not. But if they're lingering around for another 3-5 years, then I say it's worth the effort.

I am going through the same issue to stay Sierra or go Mojave. I did not go to High Sierra because of the division on whether the drives would be APFS or stay HPFS. I now have not problem going to Mojave and most of my departments only use 64 bit Apps. Exception is my Music Department and running Apps like Pro Tools. I want to go forward with Mojave and convert drives from HPFS to APFS using Jamf Pro PreStage Enrollments and DEP. However, my machines are 3 years old and I no longer have Apple Care support so if anything goes wrong during BIOS updates its on me. I will decide in the next month what I am going to do for sure. I have a plan to use Jamf Pro to push via Mac Store Apps the Application Mojave and then I can use Self Service to create a script to wipe the drive an and re-install Mojave. The only issue then is Computer Name has to be changed manually before I add to AD.