As for your question, it's possible. Gagne won the NL Cy Young in 2003. Last closer I could remember who won over the past two decades. Don't even think Mariano won a Cy Young.
Gagne in 2003 posted a 4.7 fWAR and going a perfect 55 for 55 in saves along with a 1.20 ERA and 14.98 K/9 (137K's in 82.1 innings).
You figure Miller would have to reach 50+ saves and ERA in the low 1's or below 1 and for sure 120+ K's and needs to post close to a 5 WAR season.
Also, some weak competition from other NL arms like Skenes, Yamamoto, Alcantara would help go a long way.