You won't have any idea of what snow conditions will be like till maybe two weeks from your start.
There was a lot of discussion about it this spring (2013) because there was apparently a much heavier than normal snowpack that lingered quite a bit later than normal.
It will depend on snow conditions whether you will be able to follow the route, or if it will be hard enough to walk on (with much variability in the course of even one day).
Weather conditions will also dictate. Low cloud conditions (think thick fog where you'd lose your hand if it wasn't attached) can cause disorientation. Rain or snow may make conditions unsafe. You won't know till the day of.
I'd consider laying alternate plans in the event Napoleon won't go. One idea might be to start from Irun and follow Camino Vasco del Interior till it connects to Camino Frances.