Am I required to return sabbatical payment if I do not return afterward?
You will probably have a contractual obligation for one year. You may even need to sign a document affirming it before you can be paid. Talk to someone at your institution to learn the rules and the consequences of not returning. You might want to find someone outside your department if you don't want to signal your ambivalence. 

You might also consider that any new institution might not be pleased if you step away from an obligation at the old one. No way to be sure, of course.