Well, on a systemd-based distro, you can

    systemctl hybrid-sleep

And configure it as the lid close action trough logind conf (or your DE's). It works differently, though (AFAIK). It saves the state to both RAM and disk, so when battery eventually runs out, you can resume from disk. The solution you offer seems interesting. It would just need a RTC wakeup event, so that the system goes all the way to S5 after a set time.