When my son graduated back in Nov 2012, we bought 3 non refundable ticket. After talking with the airline, they told us if for some reason he got pushed back that we could still use the tickets for another day, just had to pay a small additional cost. I believe it was $50 for each ticket which wasn't much considering the cost of refundable tickets. Check with your airline and see if it works that way for them.
Southwest allows you to change your flight without a charge as long as you change at least 24 hours before the flight and you would have at least that much notice. If Southwest is not an option for you, the fee to change tickets is usually not as much as the difference if buying nonrefundable tickets. Check the fees and then make your decision. See Saving Money PIR Weekend for within Boot Camp Moms (and loved ones) other ideas. I also invite you to join that group while you are there and to check out the other Pages (found under the pictures of the Members) as well.
There is no way to predict if your recruit will be one of the ones who has a problem that pushes back or prevents PIR. That is an individual thing and happens due to injury, sickness, failed test, or attitude problems. The RDC's do push the recruits to be ready on time for PIR, but things do happen for some. Around 86 recruits are in a division when the division forms, but around 75 to 80 will actually have PIR with the division. Encourage your recruit to do his best and believe that PIR will happen on the scheduled date.
I just couldn't afford the refundable so we waited until two weeks before his scheduled PIR and took a chance and made our plans. My son had told me that he was passing all the tests up tell then. I was very nervous for the next week until it got the I am a sailor call but it ended up working out for us. He knew for SURE 8 days before. We leave tomorrow and I get to see my son Friday!