Yes - Collins and Murkowski will not vote for Amy Barrett, though I think Trump is holding her for RBG’s seat to at least take the gender out of the direct attacks that will come. After the midterm and Republicans have a much more solid majority in the Senate she can be nominated.
That being said - what has happened to Kavenaugh will look like child’s play. Trump’s people need to get out in front on this one, they will attack Barrett, her husband, her parents, anyone with a close connection that they can assert she hasn’t distanced herself from. Her husband will especially be the one at risk.
It is not inconceivable that Trump will get at least two more shots, RBG can’t last too long, and in his second term Breyer will try to tough it out but he is already 80 years old. Thomas is 70 and could easily make it through the Trump era, but he may decide to retire while still young enough to actually enjoy a retirement while also enabling a much younger person to extend a conservative view for many decades.
Samuel Alito is 68 years-old.