You're right, bugging out with a disabled person without a vehicle is a last resort. We're all wrong though, to assume that the person's electric wheel chair is a viable bug out vehicle to move them. You can't rely on the electric charge, and when it dies you are pushing a 250 lb item up and down hills, over alot of ruck, through snow, among traffic etc. Non-electric wheelchairs are lighter but better to leave the wheelchairs behind, and move the person on some other conveyance. Pictures of refugees show alot of innovation in how they will move, even pushing sedans filled with family and stuff along the road once they've run out of gas. Frankly that wouldn't get you anywhere in the Pacific Northwest, not with our predominant hills and our wet. So you need to think light, and that's why I suggested a nursery wagon, which has a capacity of at least 400-500 lbs and can accomodate at least 1 disabled person with additional gear and infants. It also has a steering bar that could be modified to be towed by a bike (maybe), or broadened to be pushed by two adults (easier). And you might strap a walker on, they're pretty light and compact, ensuring the person some mobility at destination.

But all in all, the best plan for success goes to Mr Wildman: plan ahead for a bug out destination, ensure ou have access to a vehicle for you and your charges, and leave early as a precaution (cost = some gas, maybe a couple nights in a motel or imposing on friends or family, some time off work, peace of mind and a successful evac = priceless).