The answers above are pretty good, I'll add a few things:
WAI draws a lot of bleed air from the engine - far more than ECS or Engine AI, so the potential impact to EGT margin is large. Further, on some Boeing types, WAI don't work if the slats are deployed as it opens the cavity that the WAI air is heating (not sure it that applies to the 777).
Oil quantity is 'advisory' only, and is not the most reliable or accurate measurement on the aircraft. An engine should never be shutdown in-flight for low oil quantity by itself - rather it's an indicator that you need to keep an eye on oil pressure and temperature. So long as they remain normal, no action is required.