If you purchase your train tickets early and your flight is delayed thus missing your connection. Do they honor your ticket and rebook you?
Swiss full-fare train tickets are good for any train running the route which you booked. In other words, if you miss the 9am train you can simply hop on a subsequent train ( 9:30, 10am, 10:30am, etc.) that goes to the same destination during the same day.
Since there’s no cost advantage in pre-purchasing full-fare tickets, you can also just wait until you arrive in Switzerland to buy them.
There are train ticket offices inside both the Zurich and Geneva airports where you can discuss your itinerary with the reps at the counter to figure out what train pass options best fit your plans.
You can also buy single train tickets right at the airport and start your trip from there.