This thread has morphed into a discussion of the benefits and objectives of disaster planning. This is good.

Any options will have pluses and negatives. Some, given current situations, will be more or less feasible. Some will be superficially easy (hop in the car and drive 400 miles) and others will be extremely difficult (walk the same distance). Walking is worth considering because it requires little gear, although a lot of ability. It might be worthwhile when the roads are clogged or otherwise unavailable.

One might reason, "Well, I certainly can't walk 400 miles today. What needs to change so that I might?" Obviously, one needs to start walking and training. One needs to acquire lightweight gear and the expertise to use it properly. If one puts forward the effort, the walking option becomes more feasible. If one doesn't, hopefully measures will be taken to improve other options (get a really good vehicle, enhance bug in gear, etc).

Getting fit so that long hikes are possible leads to better fitness in general if that is the option taken. From personal experience, I can testify that this can really help. At one point in my life, I was deeply involved in wilderness SAR. This lead to regular distance running - at first about two miles, and later, to training and running marathons on a regular basis. All this made me much more capable in the field and benefited me in many ways not related to SAR.

The best course is to start for your destination with vehicle, but with the means and capability to shift to bicycle or foot if circumstances change. That way you are truly equipped to survive.

Basically, thoughtful planning and consideration of improbable options can lead to entirely new perspectives and capabilities. The glass is either half full or half empty. Just be sure you check before declaring it to be completely empty.

It should be pointed out, discussing heavy walking along the Oregon Trail and the handcart pioneers, that their option was not at all devoid of risk. It took a lot of time (six months or so) and I understand mortality rates ran around 30% - you would have better odds if you enlisted in the Marines for a tour in Afghanistan.