OP, sorry you are put in this situation. Like most responses, however, I do feel the best thing is to stay out of it the best you can with few open ended questions to get them (your dad) thinking about what he would do if money were to run out.
I have been in your situation and am still in your situation. Ever since I was 18, I have worried about what my parents' retirement would be like. I always get "don't worry about it", "the government will take care of us", "we'll just eat less", etc, whenever I try to have discussions about their expenses. They have also supported my siblings through most of their twenties and are still supporting my brother, who has mental health issues. Trying to have discussions regarding their money has proven to be stressful for both parties and probably created resentment on both sides. I have tried to talk to my sister as well, but I think that it just drives us apart and makes her view me as another parent rather than sister/friend.
For the last few years, I have learned to let it go a little more. Well lo and behold, they need to retire soon since they can barely work due to health reasons. I just found out my dad owes almost as much in credit cards as he has in retirement! I almost keeled over! My parents are starting to realize they don't have enough money to live on. They are thinking about selling some properties that may bring in a small amount of money (properties that they wanted to pass down to us). They may have to move the a lower COL area (where we are) and sell/rent their home. They are thinking of ways to cover for expenses that they never considered before. So like others said, most people will figure out a way if push comes to shove.
With that said, I don't disagree with you that their choices now will likely become your problem later. Until then, you can't do much. I also grew up with mindset that I will need to help my parents out. So, my DH and I are planning on paying off some of their debts, but not without certain conditions since it is now our business. I am going to be making an appointment for a financial advisor to help them with budgeting and try to see where they can cut out some expenses. I have told my mom that I can't help them if they can't help themselves. My sister, on the other hand, will need to marry someone with money since I probably won't give her a dime.
My advice to you is it is ok to discuss your concerns with your dad, but not with I think you should do this or that attitude. In the meanwhile, it is not really your business until you are paying for their expenses. So, continue to do a great job at your work and save as much money as you can. When the time comes and they need help, you may be able to afford to do so without hurting your own financial security.