The major concern is whether or not your current roommate is counting on you to be a future roommate. If not, then best to keep quiet about future plans as they may change. If so, then you should be clear that you will not be available as a roommate next year.
Happens frequently with freshman as one roommate may join a Greek organization or prefer theme housing, or one may plan to study abroad, go for a single room or transfer to a different school.
Reminds me of my college freshman year when three of the nicest & most interesting classmates held guaranteed transfer options for Cornell University. All were open & honest about their situations.