If they stick with Kamala, it means the Democrats know Trump cannot lose.
They won't want to throw away a more valuable, capable candidate like Newsom in a contest that they know is unwinnable. They will let Harris run and lose and she will drift off into political oblivion. No great loss to the DNC. Then, after Trump's term is over in '28, they will use Newsom against Trump's successor.
If they have any hope that they can beat Trump, the Democrats will drop Kamala, but if she stays in, it means they know the election already belongs to Trump.