The law will not enforce an illegal act. However a easment by percription may be what you are talking about. You need to sit down with a lawyer right away to find out what is going on, if you are being sued.
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I agree with Shawn. Get competent counsel right away. Your inquiry could be used as an 'issue spotter' on the bar exam.
In addition to prescriptive easement, there may be easement by necessity, zoning, inverse condemnation, and bona fide purchaser rights issues at play here.
Moreover, what happens if the earth does move? It is almost a certainty that any injury caused would be disclaimed by your homeowner's insurance. Now, you might be willing to bear that risk for yourself, but what if your neighbor seeks damages against you. Or how about this one? Post- slide, your neighbor claims you have the sole duty of reestablishing access. They don't call it a servient or burdened estate for nothing!
Good luck. I hope it helps.