Is there a way to open screen's terminal scrollback buffer in vim?

From within a Screen window, run

screen -X hardcopy -h s
vim s
rm s

hardcopy -h dumps the scrollback into a temporary file which you can then open in Vim if you like. If you script this you should use a proper temporary file name:

#!/bin/sh
scrollback_file=$(mktemp)
screen -X hardcopy -h "$scrollback_file"
vim -c 'call delete(@%)' "$scrollback_file"

(Or you could just run your shell in Emacs or in Neovim.)