I've planned this A LOT. Not because I have any intention of doing it, but because I like the thrill of the scenario.
I could easily get a few days headroom by telling DH I was going to stay with my parents. I'd need my phone switched off at this point (I'd be switching to a burner), so I'd tell him I forgot my charger. That would give me around 3 days before the alarm was raised.
I'd also have to take my car somewhere because it would need to have left the drive way. So I'd park it down a track, concealed by thick vegetation.
I'd then be disappearing on foot, from our front door. We live in a town surrounded on all sides by tens of miles of countryside. I know where there are no cameras and hidden barns tucked away on farmers' land, which I could sleep in for days.
During this time I'd be dying my hair dark brown with a box dye purchased for cash many months earlier (you can imagine the scenes, doing a box dye job bent over a cow trough!)
I'd make my way through national parks, sleeping in bothys, wild camping and living off the land. I could certainly get away with it for a few months, before working out the longer term plan.