I too see a uphill battle in trying to sue and win , the tree root problem was not that recent BUT the Op is free to choose to try to sue. When the sewer line had failed at the duplex that I had , it was just a few months after I sold it to another party , that was the one that had its sewer pipe go out the side of the basement wall into the basement of the house to its north since they were shared sewer and by the time that house to the north had been torn down and the lot was not re built on its really hard to say even if the vibrations from the tear down helped contribute to the failure or not, granted the duplex that was torn down was a real eyesore, the one neighbor Hattie who had grown up and lived all of her life on that block told me its history and about what year he bought it and converted it into two units and that he had given it to his son John as a college graduation present , John didn't spend a nickel on it unless he was ordered to by the city so when the last round with inspections was done he chose to tear it down rather than comply and he also didn't tell the demo company it was on a shared sewer so the demo guys were surprised when I called the city and a guy from public works told them they had to protect that sewer line. ( I don't think they even capped it , seems to me they broke it off further in and carefully covered it with a piece of foundation wall ) so long to short by the time the line failed the city allowed it to be patched instead of a new line being dug in and installed directly out ,it would also have its own tap card , the one I sold it to didn't point a finger at me either , they had lived there during the other homes tear down and just accepted it as one of those things.