If he kills the tree, it will still be as large as it is now and this time next year in high winds, will come crashing down. Not to mention drilling a hole in a neighbours tree, has some difficulties. Good idea though.
I remember seeing somewhere that if a tree is planted after the house was built and land designed that, should the tree cause structural damage to a neighboring property (drains, sewers, foundations etc), that the tree owner is liable for the damage. Can't remember where I saw it though. Contact...