Odds are they didn't know of the failure until the gear was already retracted.Worst case scenario at that point would be damaged gear and/or damaged skin around the gear increasing drag. An increase in drag (damaged skin) would reveal itself when you got to the TOC and checked your fuel on board. If subsequent checkpoint match the flight plan fuel, then odds are you are fine to continue towards your destination while decreasing your landing weight.
I worked at 2 companies where the exact thing happened and each handled it differently. The first company chastised the crew for continuing and the second company used the crews' decision to continue as a great example of maintaining safety WHILE satisfying the passengers.