My daughter has been pretty good at doing 25 mile rides with my wife and I since she was 8 (she just turned 11 - when she ups up to a bigger bike, she'll probably be able to go farther). She's a pretty lazy kid too (aren't they all now?). But she's pretty good with the 25 miles. With a PB&J sandwich at the midpoint and a candy bar break at mile 20 to prevent an emotional breakdown, she's good, stays with the pack.
I guess when SHTF, convenience takes a back seat to dependability. A properly setup bike should be able to get you almost anywhere you need to go. Just make sure you bring some chain lube and metric allen wrenches.
Yes, I can see the sense to this, it just hasn't been my experience that it works all that well. Of course my youngest boy is a special needs kids, and that causes a whole second set of issues with bugging out to begin with. My older boy is pretty good about things, but he and my wife are not in the same kind of shape I am in, and I bet once the stress of bugging out hits, I am going to have a really hard time to keep a pace they can all match. Not only that, but the drive to get to our "safe haven" will make it harder.
Add in traffic, and drivers, people trying to get out themselves that dont have a bike and think yours looks pretty good, and all the other stresses of that situation, and you could have a lot of problems that would be avoided by being in a truck or car. Of course the flipside is making sure you have a way of getting something the size of a truck or car to where you need/want to go.
I have racked my brain on this subject, talked to dozens of friends and people about it. We got a hybrid three wheeled bike for my youngest, which he loves to ride, and have tried a number of times to put some sort of plan of action together on how to make this work. Bottomline (from my point of view) is that you are multiplying the issue and possible problems by taking one group in a truck/car and turning it into a number of solo targets. Even at the best of times, keeping a group of bike riders together can be a challenge.
If it was me, going it alone, I can see using a bike 100%, it would actually simplify a lot of things like not needing gas, or if properly equipped, even a trail. As a family, it is a huge risk.
(Sorry all, got long winded... :O )