But the question is, if Republicans did not think Democrats would end the filibuster, would any Republicans support ending the filibuster? If the answer is no, then why not?
The answer is because it is the wrong thing to do. The filibuster is another check and balance to ensure congress, or one party, cannot do anything to disruptive or destructive to the country with just a small majority.
If Republicans end the filibuster they will pass all the legislation they want or believe is necessary. But if Democrats win a small majority in the Senate and the House they will simply reverse all the laws Republicans put in place when they were in power. There will be nothing Republicans can do to stop them.
Take this budget situations today. Republicans will defund NPR and PBS, Planned Parenthood, illegal aliens health care, Obama care, etc. If Democrats win in 2028, they will put all that back and for 4 years Republicans will be stuck.
The fear is Democrats will end the filibuster themselves and pack the courts, pass laws mandating unsecure voting practices, making PR a state, funding all kinds of liberal causes. etc. But they will do that if they get in power either way. I don't see how it helps Republicans to end the filibuster themselves. This is an argument that Republicans can win. Democrats shut down the government. Make them own it.