Boomers:
IRA's or 401K's don't have to be stock. Thus, irrespective of who funds them, if people move them to cash or bonds or tbills, the markets can get just as hammered.
As to the boomer question, my own theory has always been that boomers will start to take money OUT of the markets to PROTECT their retirement. That's just common sense and is retirement planning 101. When you are 25, you put 100% in stocks. When you are 65, you have maybe 30% in stocks. Since boomers are so rich (relatively speaking), I suspect they will not hesitate to protect their assets if their retirement is at risk.
One other issue that I've always believed about boomers is that (and this was before the housing bubble even happened) boomers will downsize like crazy. So many boomers have 4,000 square foot homes, lots of yard, pool, decks, etc. It is just wayyyy more than they need as the last of the kids moves out. I suspect the day will come when they (by the masses) want to unload those monster houses and get a maintenance free 2 bedroom condo. When that happens, housing will get killed. Of course even apart from this theory, then came along the bubble. So, if there wasn't enough pain left in housing anyway, boomer retirements will add to it. Should be a major trouble area for many years IMO.
Len