PA, on the basis that the results haven't been released,
a) you're 'covering all the bases' if your DS doesn't get a place, assuming you're put St O's as first preference?
b)If you haven't put it as first preference, and he scores highly enough, they are likely to write to you independently asking if you would consider sending him there.
c) If neither a) or b) apply, you can certainly go to the front office and they will look up the scores and position for you (I went, out of interest, 48h after 'D' day).
d) Some independent schools will give you leeway, some won't (2y ago, acceptance date 1st March, 11+ results not available until 2nd) - you will then have to consider whether you spend the money making a deposit / agreeing to a term's fees..
It's worth ringing the indies you've been offered places from, then you know where you are...until results day...