Spoiler Alert: This post contains spoilers from the Season 5, Episode 14 episode of “Yellowstone,” “Life Is a Promise” which premiered Sunday, Dec. 15 on Paramount Network.

Kevin Costner’s early departure from “Yellowstone” killed the show.

It happens with nearly every series put in that uneasy predicament. No “Office” fan cites seasons after Steve Carell left as their favorite. “The X-Files” fizzled once David Duchovny left. And although firing Kevin Spacey was the right call, Netflix’s final season of “House of Cards” without its lead was forgettable.

Meanwhile, Costner made an unfortunate gamble on himself, leaving the lucrative “Yellowstone” after the first half of Season 5 to focus on his big-budget vanity project, the film series “Horizon.” Cut to the end of 2024, where “Yellowstone” still has huge ratings, whereas the first “Horizon” was a box office bomb and the second lacks a theatrical release date.

Despite being an unwise fiscal decision, Costner’s departure seemed final,...