Yeah it depends on the persons situation. I've seen people with 5-10 properties with no debt who wouldn't sell as everything will become part of their estate, that said as a percentage of value the rental yields on some are shocking. These folk will generally have other assets (anything from cash, bonds, shares, commercial, farmland, etc) so retirement funding is no issue.
On the other hand I have seen alot of 50-60 year olds with the family home and an investment property with varying degrees of debt, some will sell while some will try to get by without. Some may sell and payout the family home loand (if any) & others will downsize. I think it is a real mixed bag.
It can be argued back and worth about if BB will sell in mass or not but one thing that is fairly obvious is that these age groups will not add to the net demand for property, if they buy something it is most likely something else has been sold (downsize, seachange)