Awesome advise!
If one spring has snapped and you suspect the other to be just as bad, the ONLY course of action is to replace both, however if you are more comfortable taking left hand bends faster than right hand bends then the nearside spring should be ok and therefore just replace the offside one.
If you sell the car and the other spring goes shortly after you have sold it and there is an accident you may be held accountable for selling a vehicle with a known defect. Especially now you have asked the question on here.
Personally if i have any doubts about something not being wrong then it will be investigated before i use the car again and if that means being without a car, so be it. Id rather have to buy another car than be in an accident with my kid in the car.