If the train is obviously going to arrive past the connection time I would tell the conductor. He *might* be able to get the conductor to hold 704 (explain that you need to catch 704, to connect to the bus to Visalia). But I doubt that they would be willing to hold the 704 for long (maybe 5-15 minutes.) He also might be able to get the ball rolling sooner for your alternate routing.
If you miss the connection, go speak to a ticket agent in Sacramento. They can either ticket you on 718 and get a cab to take you from Hanford to Visalia (there's no bus that connects with 718, so you'll need a cab) or if the train is really late, they will put you up in a hotel in Sacramento overnight and ticket you on 712 (you'll take a bus from Sacramento to Stockton).
If a ticket agent can't resolve the situation to your satisfaction... then I would call Customer Relations.
Bottom line... if Amtrak blows your connection to 704... it's Amtrak's problem and they will fix it for you, for free.
Also if it's not too personal, may I ask what brings you to Visalia? I worked in the Central Valley for almost 4 years and got to know the town quite well. It's a lovely little city, but not exactly a tourist hot spot.