Even if it is his property he cannot just up and rescind your rights to use it.
If he didn't know that's one thing but if he did know and kept it secret during the sale that's another. if he can be jinxed into making a statement of record that he knew and had informed the previous owner, and the previous owner did not disclose it then you can sue him or his estate and the title insurance should cover such a thing.
One thing I remember from real estate law is once an easement has been granted unless it was restricted by a contract it is deemed to be somewhat in perpetuity.
the neighbor obviously allowed the previous owner of your lot to make improvements by lack of knowledge or by granting easement which could have even been word of mouth.
If your real estate tax appraisal shows the land under the improvements as yours and you have been paying the taxes, and his tax appraisal does not include that land in his tax liability you might be able to have a court award ownership by adverse possession or at least order that the present easement remain for the life of the improvements.
Escheat is a common law doctrine which transfers the property of a person who dies without heirs to the crown or state. It serves to ensure that property is not left in limbo without recognized ownership. It originally applied to a number of situations where a legal interest in land was destroyed by operation of law, so that the ownership of the land reverted to the immediately superior feudal lord.
As per real estate law (varies by state) if there can be established some form of abandonment ie failure to pay taxes, failure to annually challenge any unauthorized use, the ownership rights can be ruled to revert to the State and then be awarded by the court to the person with the next highest and best claim in the real estate.
If the neighbor had at one time granted easement then it would be by the conditions of the contract or if a verbal agreement then usually the courts rule the easement stands for the life of the use or the improvements.
If the previous owner granted easement or sold the land to your previous owner and your neighbor is unaware of this then he would have to sue the person or estate of the person he bought his house from for not disclosing it.
I find it highly unlikely that the neighbor would have gotten a loan to buy the place without an assay and appraisal of the property. it's one of the mandatory due dilligence requirements of the loan and title insurance.
In sort once an easement like that has been granted for any reason it is deemed to exist for the life of the improvements. the property owner cannot just revoke the easement because he doesn't like you or what you're doing with it.
And he can't revoke the easement because he changed his mind or because a new guy owns the property.
He can challenge new improvements but he cannot restrict you from using or maintaining the improvements.
I would:
Get a legally binding appraisal on your place and get copies of previous tax appraisals and assays of your property and his.
then figure out who legally owns it as per the land patent- deed and who's been paying the taxes- the deed, the tax assay and the legal assay and the legal description might not all jive....
If it's his and you've been paying taxes in addition to the maintenance etc, and he has not been taking legal action to secure his ownership against your use or the previous owners use the propert can be considered abandoned.
certain actions are required of an owner without their performance can be ruled abandonment.
you have to pay the taxes
you have to maintain your ownership ie make sure the public knows it is yours and fight off (leagally) any squatting or unauthorized easements.
simply mowing the grass putting up a fence or making and maintaining improvements on someone else's property does not constitute abandonment by the owner.
your actions cannot constitute abandonment, the owners inaction is what constitutes abandonment.
If it can be proved the owner knew there was an easement, did not inform you or the previous owner for several years (should be something like a "statue of limitation")
and did not challange your enjoyment of the property during this time then it can be rules he abandoned his rights.
according to real estate law most states no longer recognize alloidial estate you don't actually own the property, you own a package of rights to use the property.
The real estate was acquired by some sovereign governing authority by war or by treaty or purchase and then subdivided by legal description and assay and then a package of rights were passed from the governing authority to the first owner of record, his heirs and assigns by land patent recorded as a deed in the county registrar's office.
the land patent on any piece of real estate should have a link-chain of ownership all the way back to the governing authority that first took possession of it.
you can sue him for ownership or to prevent him from aggressing your easement of his property.
You should have nothing to fear from the law
