If you're not willing to provide adequate vet care when needed then guinea pig's are not for you. Not many guinea pig illnesses can be treated in home and they are extremely painful. In my opinion it is extremely inhumane to sit and let an animal suffer because you cannot or will not take it to the vet.
To add, yes, humans and animals have lived for hundreds of years without medical assistance but that doesn't mean that they had a good quality of life. Animals that go without medical care when needed will live significantly shorter lives. Modern medicine has made it so we can live much longer and healthier lives.
who are you :?: