Am I responsible for informing my employer that I’m no longer eligible for benefits?

I work for a company with around 300 employees in Oregon. I have been receiving health insurance benefits for several years, but I’m about to drop my hours below 30, which will make me ineligible for benefits per my employer’s policies. However, our management is currently in complete shambles, to the point where I don’t think that HR will notice my change in hours for quite some time.

My question is: if they keep me on the health insurance plan for some time after I become ineligible, is there any risk that they could come back and demand that I pay them back for their contributions towards the premium? Would it be legal for them to do so? Or is it firmly their responsibility to track my eligibility and if they take a while to catch on to it, that’s on them?

Please don’t respond with anything along the lines of “that’s wrong/unethical so you shouldn’t do it”. I believe health care is a human right, it would help me greatly to receive another couple of months of insurance coverage, and financially it’s a drop in the bucket for my employer. I’m not looking for an ethical discussion, just information about who’s responsibility it is to make sure my health insurance is terminated when I become ineligible.

Grateful for any insight on this topic!