The Cubs have never really had a lot of lefty bullpen arms and depth is still a concern in that regard. Luckily, most of their lefty relievers will be at Tennessee and Iowa to start 2020 and they should all get some big league experience in the first few weeks of spring training.
While this post does not have a “Most likely to succeed” tag, the Cubs will have several choices should they need lefty help. That doesn’t include Justin Steele, who is currently a starter but might move to the pen this year. If that eventually is the case, you can move that 95 mph fastball and beautiful curve to the front of the line.