JC: I get your character and personality and I’m sure you are very sweet. But… you are in a tight spot right now.
IMO you have a case against your neighbor. If you win, you will recover atty fees in addition to the repair costs.
Please speak with a real estate atty who has litigation experience ( not transactional- ie drafting contracts ) This consult is free. He/she will advise if it is worth pursuing at this point or you simply have to bit the bullet and pay for repair yourself.
You have one shot at collecting against neighbor — when the house sells. You must prevent the sale by filing a lawsuit in Superior Court and gain an injunction to cloud title and stop the sale.
Guy is very motivated to sell as he will be shipping out soon so you have to act quickly.
Please, skip the mediator. They are simply running out the clock until the guy leaves. At that point, you are SOL.
Even if you ‘win’ in small claims or mediate some deal, trying to collect from someone that is moving away will be a literal nightmare for you and probably will result in nothing collected.
Again, I get you are a nice person but signage and pinging a realtor won’t be effective. Call atty tomorrow and get advice and let them do the heavy lifting. It is time to stand up and be strong. You can do this!