Given the package the Cubs gave up to acquire Chapman combined the potentially small window of opportunity to use him before he becomes a free agent, it is no surprise that he has been slotted in as the new closer, replacing the incumbent Rondon.
Fantasy Impact
Rondon did not lose his job due to being bad at it, and the odds are pretty solid that he will continue to provide very good ratios and strikeouts for a reliever. If your league allows benefit from Holds, then Rondon remains a solid reliever for fantasy. If it only counts for saves, then he loses his prominence and becomes a supporting player you might use if you have problems with ratios and can make daily lineup selections.