Should i warn my 4 year old that the dog will probably p away soon?

Ok my 4 year old daughter absolutely adores my parents 12 year old dog. She sees and plays with him almost daily. Her attachment to him has came about just in the last few months. Before that, she liked him but wasnt as "obsessed" with him as she is now. She constantly asks to go see him and says things about the future and includes him. For example, she always talks about when she grows up and has a car shes going to take him for rides. Well his health is steadily declining and im afraid it wont be long before he pes or has to be put to sleep. I dont know if its better to warn her now that hes not always going be around or deal with it when it actually happens. This will be her first encounter with losing someone (human or animal) and i want to make sure i do this right. So when she brings up the future and includes the dog, so i just go along with it or try to explain that he wont be around forever?