Some people (like me) prefer to use the default X cursors over the "improved" adwaita ones, so you should leave a choice there.
You should add these lines to postinst:

    update-alternatives --install /usr/share/icons/default/index.theme \
    x-cursor-theme /usr/share/icons/hicolor/index.theme 10

And add a prerm:

    #! /bin/sh
    set -e
    case "$1" in
      remove|deconfigure|failed-upgrade)
        update-alternatives --remove x-cursor-theme \
            /usr/share/icons/hicolor/index.theme
      ;;
    esac
--
Please limit your reply to 7-bit ASCII.
I refuse to see your idiotic emoji in a TTY.