I really hope you are kidding but I'm afraid you aren't. This "solution" is just wrong. Does the OP have a right to be VERY upset? Of course, and I would be, too, but it isn't the neighbors' fault any more than it is the OP's. It is quite unreasonable to expect that they pay for the value of the tree and pot - it simply won't happen, nor should it. The OP sprayed a fish-based substance on the plant and it should be no surprise that a cat found this enjoyable. It would be the same thing if you grew a flowering tree and a crow was attracted to the berries and knocked the tree over. S**t happens. No wonder our society is rampant with a "sue first, ask questions later" mentality. Not everything is somebody else's "fault" that they should be expected to pay for.
The OP even said in the post that they regret shouting at the cat. If that hadn't happened its likely the tree wouldn't have fallen. So there is half the blame. If there is willful negligence - the neighbor knocks over a fence, or sprays a weed killer, etc. that kills your bonsai that is entirely different. But in this case the OP is technically just as responsible by making the animal scared and jumping. Stealing the neighbor's pet and covering your tracks (cash purchase - really??) is far worse than the initial infraction. Suck it up, express displeasure to the neighbors and ask them to contain their animal, chalk it up to the fact that the world isn't fair.