Generally ssh will just forward signals (SIGINT, SIGQUIT) to the remote host. If that side is not responsive, you can hit Ctrl+C all you want, but it won't do anything.
It's client-side, so works even if the remote system is totally hung and did not clearly disconnect.
For example, running `systemctl suspend` will not terminate active SSH connections before putting the destination machine into a sleep state, and thus Ctrl+C (which isn't processed by SSH) will do nothing until the remote host is woken up by some mechanism.