We know exactly how they’d act, since they eliminated the filibuster for judicial nominees so they could pack the court. Holding ourselves to some standard they will immediately violate when they can get any advantage is stupid.

Realistically, given a condition where it stood in their way, they’d probably just eliminate it themselves

They already killed it for Supreme Court nominees when it suited them. If they really wanted something they’d kill it for that

By 2017, roles had reversed — Republicans held the majority in the Senate, and President Donald Trump sat in the Oval Office.

After Senate Democrats, now in the minority, filibustered the confirmation of Judge Neil Gorsuch — Trump’s first nominee to the Supreme Court — McConnell engineered his own “nuclear option.”

The Republican-controlled Senate voted 52-48 to reduce the vote threshold for confirming nominees to the Supreme Court from 60 to 51, per The New York Times.

https://www.usatoday.com/story/news/factcheck/2020/10/01/fact-check-gop-ended-senate-filibuster-supreme-court-nominees/3573369001/

They can also just remove it if they have the majority

Never expect them to act in good faith. They have already repeatedly trampled norms

Practically speaking, this election cycle is the hardest for Democrats in the Senate. There are 23 seats currently held by Democrats (and Independants organizing with them) up for reelection, vs. only 10 Republicans.

In the 2026 election, barring any additional vacancies due to retirements or deaths, there will be 13 Democrats defending seats vs. 20 Republicans. In 2028, the split is 15 - 19.

https://en.m.wikipedia.org/wiki/Classes_of_United_States_senators

If the Democrats do keep the Senate and reform the Filibuster, then unless there is some radical change in political alignments Democrats will be favored to hold on to the Senate until at least 2030. There is a lot of work Democrats can do during those 6 years that might be impossible with the Filibuster in place, as it currently is implemented.

I would argue that keeping the Senate is just as important as winning the Presidency. Perhaps more so. If Trump wins but Democrats keep the Senate, they can use their power to ratify Cabinet officers to keep the worst of the worst appointments out. Likewise, if Harris wins but Republicans take the Senate, I doubt any of Harris’s judicial appointments will be approved at all.

It’s not really restraining them at the moment.

Then make them own their choices. As long as they can stick with this limbo there’s plausible deniability that no one sees. Or require it to be a speaking filibuster. In Minnesota, the conservatives had control of all the levers until they “caught the car” on banning marriage equality. At a state level, that woke a bunch of complacent people up and now we have a democratic trifecta after a lot of work since then. That can happen at the federal level too and that’s what we are learning from Dobbs.