If there is any loss, it'll be like one poster said about the Dems failing to follow the Overton window left, but I think there's another possible negative; the pendulum swing.
Without Obama, there'd be no trump1. Without Biden/Harris, there'd be no trump2. If we shift far enough left, I'm concerned how far the pendulum will swing right afterwards.
This is not to say Zohran Mamdani's win wasn't wonderful and probably the best thing to happen to this country in... probably decades. I'm just acutely aware that this country is probably going to continue to be divided and will keep doing its craziness.