What may happen if root canal is not done although it was advised by your dentist?

They will tell you it might get infected. My ex-husband was told he needed a root canal done on all his front teeth because of an accident he was in. He did not do it and they never got infected that was 20 years ago.
You don't say why you were told it needs a root canal. If it is infected or you are in pain then you should do it.