The likeliest outcome as forecasted is that Democrats will capture the House by a substantial majority but Republicans will keep the Senate narrowly.
If so, I think we will see Trump and the Republican House try to ram through as much legislation as they can before the new incoming Democrats take office in January. Impeachment is still unlikely to happen (and would still be futile; no way 2/3 of Senators vote to remove Trump from office; in fact, perhaps not even 50% of representatives in the House would vote for impeachment.) But Trump and the GOP can kiss any hopes of passing major new legislation goodbye for the remainder of his 1st term - perhaps his whole presidency.
In the meantime, a great deal of Democratic-initiated legislation in the House will probably fail to pass the Senate, and/or get vetoed by Trump.
If Trump is serious about his 2nd tax cut (the one he says would involve a 10% decrease for the middle class,) it probably would get rammed through between now and January as well.
SCOTUS and other judge nominations would remain unchanged; Trump and the Republicans would still get them passed by the barest of margins in the Senate, should Ginsburg or Breyer leave a vacancy.