You are calling my name here Reagan, asking for breastfeeding advice! LOL
I am not exactly sure what your question is so I'll just prattle and maybe you will find something useful in it.
If you are asking if he needs formula to replace the BM (breastmilk), the answer is no. However, you as the mom are the only one who can truly answer that. Does he eat well (for a baby), drink enough, etc. You can get baby vitamins and hide them in his food if you are worried about nutrition (ask your ped for a rec.)
If your issue is that he does not drink enough from a cup, he will learn. I am never an advocate of cold turkey weaning; taking away one feed per week or so is much more reasonable for both of you. If he is just now a year and relying on you for most of his liquid, you should expect some possible engorgement or swelling if you stop too fast.
Breastfeeding has many benefits that go well beyond that first birthday though. Unless you are uncomfortable nursing longer, why not stick with it for a while? Babies will definitely wean themselves, especially when you are introducing lots of new foods or drinks to them. Maybe you could try just nursing at home, but not out in public at first. (I have no idea what you are doing now, so I am just guessing) You can also try to teach him how to get comfort from you in other ways if he is a comfort nurser and restrict breastfeeding to bedtimes, for example. By beginning to limit him that way, he will naturally get thirsty and turn to the cup. You may have to entice him with a little watered down apple juice or something in the very beginning but he will get it. Also, try different cup brands. Avent makes one that many nursing babies like. And I think so does playtex. I can find some pictures if that is the question.
I talk to so many moms who fear a six year old nurser (or something like that!) if they do not wean. It is true that those kids do exist, but they are the exception and they are examples of children whose mother's allowed the child to pace the breastfeeding. That is called breastfeeding on demand, which is wonderful for some people past the first year, but very challenging or not OK with many others.
I want to congratulate you on making it this long! The benefits of breastfeeding to you and to your little ones are immeasurable, as you probably already know.
Now, if I totally missed the mark, let me know. ;)