The L factor is when a certain event comes to pass that either proves without a shadow of a doubt that Carrot is not joining or makes it safe to assume that she's probably not joining. Basically, a punctuation point that signals me to finally move on from this. I have 2 for her
The first that makes it more or less safe to assume she's not joining is if the Straw Hats land on the next island and start exploring. As long as they're on the sea it's fair game and Carrot can appear whenever. But if they reach the next island and disembark it would show that Oda is moving on from Carrot more or less.
The second that proves she's not joining without a shadow of a doubt would be a panel of her not on the Sunny. Whether that be a panel of her on a ship back to Zou, on Zuneshia itself, back on Wano, or even a Towel-style flashback where she says her goodbyes or something similar. It would be the true nail in the coffin for C4N and a sign to move on from it.