If Marcus Smart doesn't come back to the Boston Celtics, it'll likely be because the team has made a decision about how much money it's willing to spend long- term.
More specifically, they have done the math for what they think are reasonably likely payroll scenarios, and Smart's desires place him outside the math that works for dodging the repeater tax as long as possible, so while none of us (ok, almost none of us) want Marcus on another team, the possibility exists for such an outcome.