Rules are very state specific regarding well abondonment. Some allow you to keep the well provided the aquifer is not contaminated if you "plan" on using it in the future. Contact a local well driller and or appropriate regulatory authority. Do not abandon it yourself or allow the owner to do it themselves if you choose to abandon it. There are lots reasons the keep it but only if it works and provides decent quantity of good quality water. The only way to know that would be to hire a professional to come test it for quality and quantity.
Im suprised the city did not make the owner abandon the well as a condition of connecting to city water. Generally a well is considered a potential source of contamination and either must be abandoned or the park would have to have a reduced pressure backflow assembly. I would check with the city to verify. You may get stuck with the bill to abandon the well if the owner was suppose to but just never got around to it.