Typically when finishing up, onions will show a little fading and then start to fall over, bending at the neck while still green. If they're not doing this and actually dying back, meaning browning or yellowing while still keeping the necks firm, they might have had some root die-off due to the flooding.

I'm not sure what to suggest other than keeping a close eye on them and see if they recover. Maybe pick a few and make sure they're not rotten in the center.

The only harm from harvesting early is that they won't keep well and this is only an issue if you have a lot.

-Mark

I've experienced the same thing. We haven't had flooding, but it's rained almost every day. My Spanish onions matured & the tops fell over & I pulled them. But my Candy onions are like yours. I didn't know if it was because they are "intermediate day onions" growing here in "long day" territory...

Mick

Obviously, when the top is faded away and the stem is softened, there is no interaction between the roots and the top, MEANING : the bulbs will no longer grow bigger. Then there is no point in leaving the onion(s) in the ground, that in the rainy /wet soil, there is a risk of mold and rotting.