I don't think anyone can answer for you if it will be worth it or not. Only you can weigh your own personal pros and cons. But here is what I would say:
A. I don't think employment is more unstable in science than every other sector. I would guess, although I don't know for sure, that employment in accounting is more stable than the average.
B. I don't think there is a 20 year period before becoming "employable", although this depends on what you call employable. If you want to become a professor, in my experience, you would probably be looking at an average of 6 years to PhD and then do a postdoc. Yes, you will likely need to do a postdoc, but it depends somewhat on your exact field and where you want to end up. Most people I know that got professor positions were postdocs for between 3 and 7 years (but that is a limited sample).
C. Yes, you will need to go back to school and take some science classes to get all the prerequisites necessary to move on, and this will take some time. If you can do this part time while you work, that is probably your best bet. I also think that you need to get some more experience with science before you can really decide if this is what you want to do. You frankly sound rather naive about how science works. Science actually involves a lot of grunt work, a lot of repetition, a lot of writing grants and papers, and doing other things that are unrelated to grand unifying hypotheses, especially in the early phases of your career.
D. During the PhD and postdoc periods, you can choose your research topic but it will be rather specific. If you don't think you could enjoy that, it will be a struggle to get through.
Last edited by PACN
on Thu Dec 13, 2012 2:46 pm, edited 1 time in total.