Maybe Hillary knows that deBlasio is going to be indicted and may not run for a second term. But mayor of NYC would give her access to activists and money, both of which will be helpful when she runs in 2020. I believe unless her health
really heads south, she will run in 2020.
I don't think de Blasio will go quietly, but if she thinks she can get him out of the way, she might go for it. A lot of NYC residents might feel compelled to vote for Hillary to "make it up to her" after she got "cheated" out of the presidency. That being said, I still think it's a long shot. The 2016 election was Hillary's last hurrah as a powerful force within the Democrat Party. Whether she knows it or not, she's done. If she runs for office again, she'll be viewed like a once great athlete who hangs on too long in a futile effort to regain their past greatness, and instead, only embarrasses themselves.