I agree that it’s a good idea to contact insurance, but I wouldn’t assume everything is going to be covered by home insurance.
For the purpose of covering the claim, it’s import to distinguish between a sudden and accidental new leak vs a gradual leak that relates to the original leak 2 years ago, and has been present for months/years. The former is likely to be covered. The latter likely won’t be covered. Some insurers also require to be notified within as short as 48 hours of the water damage incident, while others may support claims as long as 30 days after water damage incident.
If it was me, I’d first get a reliable evaluation and estimate, including evaluating whether there is mold, what damages are likely to be related to leak, and how much to repair. I expect all of above can be done at no cost. Depending on the answer, I’d decide whether to go through insurance or not. I’d talk with agent and get information including chance of different aspects of the damage being covered and how much future premiums would increase, before filing a claim. If the expenses are large and not well covered by either party’s insurance, then it gets more complicated. I’d try to find a fair resolution with neighbor, but would be ready to get attorneys involved, if this is not possible.
Regarding roaches, roaches often do settle by sources of water including leaking water, but that doesn’t necessarily mean this leak is the cause of the roaches. The Impact of Moisture Leaks on Cockroach Infestations in Kitchens – Aptive Pest Control