I made a one way reservation for Wed. July 5th from Irvine to Oxnard which I take on a monty basis. I also got a call saying that I should immediately call the reservation dept., etc. I was put on hold for endless minutes and then decided to just drive over to the Oxnard station (5 minutes) and...
If you want up to date information regarding the track closure between Irvine and San Diego, google Pacific Surfliner travel advisories. Amtrak is providing bus service between Irvine and San Diego and the destinations in between. They do not know when regular service will be restored.