If the Democrats win 51 seats in the Senate, I predict they will use the nuclear option enabling them to pass legislation with a simple Majority. If Biden is President and Democrats keep the House and win 51 seats in the Senate, they will be bound by filibuster rules and will say "fuck it" and pass majority legislation.
Strap yourselves in folks because no matter how this turns out, we are going to see things we have never seen before in this country.