is there an actual worry about the ticket getting split or non-votes and allowing the Republican to win

Nope. The Republican candidate is perennial loser and insanely racist vigilante Curtis Sliwa. Nobody thinks he has a chance, including himself. He's purely in it for the PR and donations.

That's essentially what "vote Blue" is about.

Nope. That's their excuse to force "electable" (read: right wing and corrupt) candidates on voters who would much rather have someone who'll faithfully represent their wants and needs but scared of getting someone even worse.

Adams the fascist cop (but I repeat myself) won his primaries by a fraction of a percentage (after a full court press propaganda campaign on his behalf by both major parties and all NYC-based MSM) and they were immediately falling over each other to declare him "the future of the party"

Mamdani beats the establishment favorite in a surprise landslide and they're all pretending that he's a communist terrorist that somehow snuck in against the will of everyone.