What are some examples of a single that literally saved that artist's career?

Some examples that come to mind are Moves Like Jagger by Maroon 5 and Toxic by Britney.

We Belong Together - Mariah Carey

Mary J Blige - Be Without You

On the Floor
Hung Up

Hung Up

U + Ur Hand

On the Floor

Work - Rihanna

Mess at me not mentioning this in the OP

Dangerous Woman

Rihanna owes her life to Umbrella, guarantee she would have been dropped or shelved if Jay had to hop on a track for a signal boost and it managed to flop

thank GOD it didn't

Good For You. I really thought Selena was gonna fade out after that heart wants song. But she definitely obliterated that thought.

We Are Never Getting Back Together

Good For You.

I wouldn't say Toxic Saved Britney's career but it defiantly proved she could still get a hit, Considering She was still selling millions of albums without a top 10 with her previous era it wasn't like she was flopping, Very similar to when people call out Bey for not getting a top 10 (until DIL) but still manages to go multi-platinum

But with all the singles of "Britney" not doing well and then "Me Against The Music (with Madonna)" flopping and with all the negative media attention she was recieving, Toxic(song and video) became one of her biggest songs and put her back on the map

I honestly think roar, as well as Dangerous woman. After Katy's teenage dream 2.5+ years, the gp was so tired of her. And with dangerous woman, not that focus was a flop but last ari era she could release static and the radio would play it.

Hung Up
Living for Love

Worth It

WDKY(Stronger)