All airport lighting is interleaved. That is to comply with ICAO Annex 14 which requires that no 2 adjacent lights should both fail.
What it means is that separate circuits power 50% of each service e.g. Approach lights, Edge Threshold and End.
So the chances of both circuits failing and robbing you of all the approach lights is in to the 10 x e7 category.
EU Ops gives a table of degradation to help permit commanders decide to land or divert but it takes no account of real world command control and power supply provisions.
Sir George Cayley