I think this is a good exercise, on several levels. The physical preparedness (fitness, equipment, clothing) is a good thing to test on a regular basis.
I'm commenting on an old post now, but I'd like to add something to Montanero's point about this being a good exercise on several levels. Another aspect is that a mock "get home" done with some repitition is an excellent idea for your mental preparation.
Most things that seem daunting or overly burdensome before you ever try it, often turn out to become pretty routine after you've done it two or three times. That 8 hour car drive which seemed to take for-EVER the first time, seems to go by a lot faster after a couple trips. And that three hour walk home may seem like "a walk in the woods" after a couple times, too.
I think that's a tremendous advantage when something happens at work and you're faced with the prospect of walking home. You've done it, you know you can do it, and it doesn't scare you. You don't need to feel anxious or try to impose yourself on someone else to come get you or to feel panicked about having to catch a ride with someone. That also gives you the freedom to stay behind at work longer, if need be, say, to stay with someone who is waiting for a ride. Or if you're going to bring someone with you or walk with someone at least part of the way home, you will naturally demonstrate the confidence that yes, indeed, you can walk this way and that it's possible for the other person to do so, too.
Since we're only talking two hours one way, I don't think it's unreasonable to try and do this on a monthly basis. That's probably enough repitition to make the walk home seem pretty routine. And is good exercise to boot!