Great case to share and appreciate your honesty and humbleness in publicizing this. Plenty of clinicians above have expressed their opinion on the question you asked so I wont comment on that BUT I think it is also important to figure out why this happened in the first place. This is a common challenge when placing second molar implants, especially in the mandible. Access is typically compromised due to limited opening of the patient. Especially when using long drills, it is very difficult to position your wrist in a way to prepare the osteotomy properly and it could end up with the case you provided.
I do not pay attention to the angulation of the roots of neighboring teeth unless there is a risk of actually hitting the root with the implant. The primary factor to consider is the adjacent proximal surfaces- trying as best as possible to have the emergence of the implant head parallel to the adjacent contacts. When prepping the osteotomy, it is helpful to constantly compare the axis of the drill to the adjacent tooth contacts. I find that this helps with proper parallelism of the implant.
Again, thanks for sharing this case and please let us know what you decided to do.