The Cubs never had any intention of keeping Aroldis Chapman more than a couple months.
They felt they needed a dominating closer to win the World Series, so they paid a lofty price at last season's non-wavier trade deadline to acquire the hard-throwing lefty from the Yankees. The gamble paid off, as you know. The Cubs got their first World Series title since 1908, and the Yankees go forward with elite prospect Gleyber Torres (and three others) in their organization for years to come.
The Cubs never engaged with the idea of Chapman returning to Wrigley Field.