If we are sitting at 5, top 4 of Ayton/Bagley/Doncic/Bamba are gone, and Porter is flagged medically still, Ainge would 100% draft Young, IMO. Cheapest and best insurance policy to Kyrie's contract length we could find. It would help in no way in the negotiation process with Kyrie, but in case he were to have a change of heart again and leave, we would have Young to fall back on, and he would have 2 years experience behind Irving.
Of course if a team like Chicago/Charlotte (likely in the 8-11 range) were dumb enough to offer their unprotected 2018 1st for a swap with us at #5, I think that would be enough for DA to pull the trigger, and get another swing at a Tatum-esque return.