If one side packs the SCOTUS, could the other side unpack it if/when they assume control?

The size of the Supreme Court is defined by a piece of legislation enacted shortly after the Civil War.  It can be changed with another piece of legislation.

Using that law as a limiting precedent, the reduction would have to be by attrition - by simply not replacing Justices who die or retire.

So no, it is generally accepted that there is no way to remove Justices from the court by any means except impeachment.

Even if term limits were enacted, they wouldn't apply to any Justices that are already serving.

Probably not.  Most likely is an overpack.  Which would then be overpacked again.

What is needed is a judicial reform amendment.  When lifetime tenure was inserted into the constitution in the 1700's, it was rare indeed for someone to live into their 70's, much less late 80's+.  Now both parties appoint 19-year-olds (I know, I exaggerate) so they can sit on the federal bench for 146 years (again).  Time for term limits.

No.  But they can add still more Justices to pack it in the opposite direction.

They can't remove justices except through impeachment.  And that's not likely.

The Dems are considering expanding the court under the next Democratic president (i.e. in a couple of months).  They could increase it to eleven or thirteen or even fifteen justices, and of course the current (Democratic) president would get to fill all the new seats.  Of course the Dems would also need to take the Senate for this to happen.

Actually I like that idea.  FDR tried to do it, and was unsuccessful.  But from an OBJECTIVE point of view, Republicans have been putting right-wing extremists on the court for decades, while Democratic presidents, Clinton and Obama, have picked moderates and centrists.  I think we SHOULD have a relatively centrist Supreme Court.

Supreme Court Justices are appointed for life or until they choose to quit or retire.

A Supreme Court Justice can only be removed via Empeachment. 

If they had the votes, they could impeach justices. But keep in mind that requires a successful impeachment by both houses. 

it seems impartiality is dead