A vet is the only one who can determine whether it's life threatening or not. But if you take him it, the vet should be able to tell you whether or not it needs to be removed. Many pigs have fatty tumors that are benign and can be left alone unless they're in areas that make it painful or difficult for the pig. Others could possibly be abscesses, and removal or drainage isn't a horribly expensive process. But abscesses do need to be drained, or they may burst and spread infectious material all over the place. Sometimes lumps are malignant, in which case they need to be removed.
But removing something that's under the skin and isn't attached to the muscle is usually an easy process. I hope you'll take him for an examination and at least see what's going on.
