Not sure I follow all this but if the fence makes any sense do it. if the irrigation is on your side of the fence just dig in there and cap it off for now. If their irrigation is crazy and they don’t adjust for your new fence the fence is going to get damaged or wear out form all the water, so keep that in mind with the fence.
I think they just took the plumeria down to say that if the can’t have it no one can. You probably have a chance to get through this with out major trouble if you are patient and take it in small steps.
Sorry if I am off on some things. I want to be helpful and have a similar struggle going on but don’t want to read the whole thread.