This is one of the parts of the job for which you're never really trained.
Every so often, usually around this time of year, an adjunct who knows he's not coming back next semester simply vanishes. No grades turned in for the Fall class, no responses to emails or phone calls, just 'poof.' (I've never seen this happen with someone who had classes lined up for the following semester.) With no realistic prospect of continued employment, our short-term leverage for getting grades turned in is pretty weak. ("Give us the grades or...uh...just give us the grades!") Most people are professional enough that even if they don't like the pay, or the non-renewal, they still make the distinction between the students and the institution. But 'most' isn't 'all,' and the damage is real.
Most obviously, students are denied the timely credit they've earned. Sometimes that doesn't matter, as long as the credit eventually comes through, but sometimes they need it right away. Falling below the threshold of "successful academic progress" can have consequences for financial aid, academic probation/dismissal, and employer reimbursements, among other things. Delays in posting grades also hurt students who are sending out transfer applications, since deadlines are unforgiving and receiving schools generally assume that any glitch in the application reflects on the student. And it wreaks havoc with any course in a chain of prerequisites, since nobody knows who passed and who didn't.
In terms of getting back at the college, the extra work generated by late grades usually doesn't fall on the intended targets. The registrar's office does the on-time grades through 'batch' processing; anything late has to be done manually. Financial aid works much the same way. (Financial aid has it worse, since pots of money can be exhausted by the time the late grades are changed.) Neither office has anything to do with setting adjunct pay scales, but they're the ones that do the heavy lifting when this happens.
The post-finals 'poof' is the worst kind. Back at my first administrative gig, I saw adjuncts walk away mid-semester. That was bad, but at least at that point it was possible to address the students as a group, find a sub, and 'look for points.' (Whenever something along these lines happens, I've taken the position that we should do our best to hold the students as harmless as possible.) After final exams, though, there's no clean and painless way to address the students as a group. At that point, too, some fairly substantial components of the final grade are typically missing -- the final exam and/or final paper or project -- so it's tough to assign any sort of reasonable value to what they can show.
I don't make any grand claims for the kind of teacher I was, but I can honestly say that doing something like this never occurred to me. Even in the worst adjunct gigs, when I soured on entire institutions, I never left the students hanging. So when someone did, I was initially dumbstruck. It was so far past reasonable that I couldn't even piece together a coherent response.
(Before the flaming, I'll just stipulate that I'm not talking about an organized work stoppage. I consider that a different issue. This is action by a single person.)
If we get through January without this happening, I'll consider it a great start to the year.