You're going to go to school while working an 8 hours/day job? Is that really going to work? When are you going to practice?
Professional would be getting paid and making a living from piano, along with some level of high level playing. The degree isn't going to automatically put you at a professional level. It's just a degree.
Professional -- High level of playing, have to get a job/jobs for playing (or teaching) that can be tricky. More options for income from small jobs, but probably less options for a regular, steady job. Have to play whatever someone else wants you playing a lot.
Amateur -- Can play and practice whatever you want. Not enough time to practice since you have another job. Probably more income, and a more steady income.
In either case, the degree isn't magic. For a pro, it's probably assumed -- at least up to a masters, but it's not the determining factor.
For your regular teacher, if you go back to school, that's how it is. I wouldn't hesitate or bother with them too much if you need to leave. Life events happen. After the degree, you could probably go back and study with them if you want.