Regardless of what happens in early November, with the midterm elections, Donald Trump will - God willing - be President until January of 2029. Let this reality guide your vote two months from now.
If Democrats gain a majority in the House and Senate, they can pass legislation (or impeachments) but can they override a veto? I doubt it. The only things of significance passed and enacted will be continuing resolutions of various types.
Meaning, literally no progress of any sort will happen. We will be stuck in a time warp, unable to move in any direction. It isn't good when the free world's most powerful and rich nation cannot act.