I wouldn't worry too much - there's a DL-operated SEA-ICN that leaves just a bit later, which will almost certainly have space for you if you misconnect.

SEA is one terminal (though the walk from end to end can be long), so this connection is easily made. If your plane departs on time there is likely enough schedule padding that you'll arrive early and will turn this into a leisurely connection. Just make sure to look up your arrival and departure gates when you land so you don't waste time wondering where you're going.