I would imagine that in most cases, we generally know if a parent has prepared for retirement or not.
I think, just as we need to have a conversation about end of life items (in-home nurse, nursing home, assisted living, etc) we also need to have a conversation about how they are planning to fund their years of later retirement.
In my experience, my parents and my MIL have saved and considered these options, have the funds to make it all happen, and (thusly) are pretty open to talking about that and letting us know that they will be okay. Certainly, we may need to help out organizing when they start to lose more of their cognitive functioning, but the money is there and the plan is in place.
My FIL, however, is and has been in denial about anything beyond today it seems. As i have stated above, if anything, his plan has been to drop hints about his theory of "familial obligation" and how many times the little kids said "yes!" when he has mentioned to them if it would be good if he "moved closer." This passive aggressive offensive reached a breaking point last visit when he mentioned that a friend of his told him, "well, looks like you need to move out there with your daughters family." He knows how we feel about this, and therefore never had the spine to ask directly about moving in.
So, at the end of the last visit, my SO had to lay the hammer down and let him know that: 1) No, you cannot move in with us; 2) the fact that you have no plan for retirement is very frustrating to us, but, in the end, its your life so do what you want. This is as much of a "discussion" that we can expect from him after trying nicely for 10 years. He doesnt want to deal with it, so we had to simply let him know where we draw the line. Now its his turn to deal with it or not.
In short, the sooner you can have the conversation, the better. If they don't have their finances in order you need to save yourself and let them know where you stand and where you draw the line. People might be mad, feelings will be hurt, rifts might set themselves in stone; but in the end, you need to do what is right for you and the children that you brought into this world.
"Familial Obligation" to me means having your ship in order and not being a burden on those around you.
My feeling is that if you have SS then you have some means of avoiding homelessness. It is your life and you alone are responsible for your decisions. If saving for your later years hasn't been a priority, then you will have to live accordingly. Sure, there is guilt in saying "too bad for you, I am retiring early," but, these are the choices we make and have to live with.