Engine light came on. Had diagnostics

Yes its law ,but it shouldnt have gone at this mileage unless you have put leaded petrol in,try new oxygen sensors in the exhaust and i think that will cure it ,Nice profit margin on a new cat for a garage up to 70% of the retail price for a dealer .50% for a general garage ,plus labour

Who told you you needed a converter? Just because the code points to the converter does not necessarily mean it is bad. It just means the converter is being effected. However if you have been driving this car for a long time with the light on, it may have damaged the converter especially if you had a miss or an overly rich fuel/air mixture. If the light is not on then I would not replace the catalytic converter at this time. If the light comes back on, which it will, if the problem was not corrected, then take it to a professional to see exactly what the problem is without guessing. Guessing can cost you plenty.

if the light don't come back on dont worry about it right now