Hard to tell. The Fake Indian's name has been bandied around for Treasury Secretary, but not sure if she'll be offered it.
The Democrat party has played a double game for 20 years, of being allegedly for the poor and more recently, socialists, while also becoming the party of the rich. As much money as Wall Street raised for Slow Joe, I'm not sure how excited they'd be to have her as T Sec, or for that matter, how excited she'd be to have to be in that position either. She's played a double game too, and if she got that position she'd be expected to carry out loony socialist goals.
As for the replacement, some states have laws that the Governor has to select from a chosen list of people, from the party the former senator was from (NC is like this I read). MA has bounced between giving the Gov lots of freedom to appoint cronies for favors when a Democrat has been in the seat, to changing it around when there's a Republican in the mansion.
Current Gov is the RINOest of all RINOS, knowing him he'd probably appoint a Democrat even if he didn't have to for political gain and kiss assitry.