One way I try to clarify my thinking on questions like this is to classify everything, and then keep each within its boundaries. The most obvious version of this is "needs" vs. "wants" (because we're very, very good at telling ourselves that things we want are actually things we need). But "insurance" vs. "investment" or "inheritance" is another good one.
Why do we buy insurance? It serves a very specific purpose: to make sure that people who are dependent on us will be ok if something horrible happens. So in your case, has the insurance served its purpose? Would your son be ok financially if you died within the next couple of years? If so, you do not need it any more, and it is ok to let it go.
Of course, you can still keep it for the rest of the term, while the cost is reasonable. If you're in a decent financial situation and not needing to watch every penny, it is ok to spend a little money on something like this. We all have areas in which we choose to spend more than we actually need to, because we value what that extra spending buys us.
But since you say you're new to this whole way of thinking, it's important to assess things clearly first, rather than just decide that it sounds like a good idea to keep this for your son. It has to start with acknowledging and really understanding that you don't actually need this any more, because your planning and saving and child-raising worked -- you did it! You got to where you hoped to be, with financial independence and an adult child who is capable of managing himself.
That means that keeping the insurance is a "want," not a "need." Which means, in turn, that you have to balance this particular "want" against all of the other things that you want. If you decide to keep the insurance, it should be because you have decided that the potential extra inheritance for your son is the best possible use of that $285 -- that it would make you happier to know that your son would have an extra $500K than anything else you could do with that money.
