IKEV2 IPSEC Autostart, restart, daemon

I assume that strongswan starts on reboot, since you don't mention using systemctl start strongswan (the command you cite systemctl status strongswan just tells you whether the service is running). If that's not the case, you need to enable the service:

systemctl enable strongswan

In the conn section you need to specify what should strongswan do when it starts and when the remote peer closes the connection or dies. So add something like:

auto=start
dpdaction=hold
closeaction=hold

The meaning of the actions is explained in the manual page. Basically you want your tunnel to get up on server boot, while if the tunnel is closed intentionally (closeaction) or because of network problems (dpdaction) strongswan will install a trap that will try to bring it back next time it is needed, leaving time to the other peer to recover.