It didn’t make sense that San Antonio would be targeted in the limited Soviet strike. It would be pretty far down the list, definitely not in the top 3. I believe Streiber has said as much, and that it was included because of the personal connection, and the reason given in the book (some military headquarters there?) was a weak excuse.
I can’t quite explain it, but it doesn’t feel right to me that Manhattan would be abandoned and salvaged like that. Seems like it would either be too dangerous for people to be there, or it would still be an actual city even if diminished. It seems like another thing done for the narrative and personal connection, to allow him to “return home” while also giving a reason he didn’t still live there.
But again, these are both minor points and really don’t detract from the work at all. San Antonio is little more than a bit of background flavor, and the story makes Manhattan well worth it.