It probably is just burned out, or otherwise busted. They are not required to be working for daylight operations (so no delays there), and I'd have to check a 777 MEL to see if they were a no-go item for night operations...
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
The 777 has 4 landing lights: 2 on Nose Gear and one on each wing root.
2 of the 4 are required for night operations and none are required for day ops.
Lamps are easy to replace. Barring any issues with wire terminals ends (which can be very common, not necessarily on 777) shouldn't take more than 10 minutes on Nose Gear. Wing mounted lights a little longer due to access.