I don't espouse this a realistic for the vast majority of people who have been laid off, fired or otherwise affected, but in fact there may be some room for some people to actually help with the teacher shortage. While there are reports of teacher shortages, they tend to come in four areas: math and science, English as Second language, urban areas and rural areas.
Just as the military becomes a more "viable" option for young people in tough economic times (although less so now with combat operations going on), teaching is often seen as a sort of viable option. But there are obstacles, the first being certification and licensure. The second is commitment--are these "fallback teachers going to stick it out?" The answer is mixed to be sure, some will and some won't but what is the difference between these new teachers and the steady stream coming from teacher colleges?
There is no telling who is going to be successful as a teacher, whether they are starting their first career or their second or third. But the unfortunate thing is that given that most teacher will get tenure by simply gutting it out for three years, means that we may get some solid teachers who go to their second career and there may be those who are just space fillers. If the economy stays bad, it can mean that we as a society lose because those space fillers with the negative motivation (i.e. being unemployed) will stick it out, marking time and collecting a paycheck.
I have never doubted that teaching is not easy, I know that it is not. I don't think it is a second career for everyone, but we shouldn't also be discouraging the notion either.