If you are to respond with an answer by 2/25 then that is your cut off date as determined by Maxwell. I have never heard of the scholarship being available after May.
IMHO it is not unethical, but it would be wrong to play that game of trying to keep it through the end of BCT. Life is about rolling the dice and taking chances. There will be a candidate that is applying only for ROTC and the pot of money only goes so far. You holding on until they are through BCT means that another qualified candidate got less or nothing at all and may not be eligible to attend their dream college. The AF is about brethren, and supporting your peers, it is not about what is best for me, and me alone.
There are no guarantees even after BCT is over. 25% of AFA cadets will not graduate from the AFA. That is reality, will your child re-apply every yr in case they might one day be in the 25% group? Of course not! You have to hope for the best, and have a plan B for the worse.
Most people when referring to plan B are speaking of the fact that they pay the housing deposit in case something happens before or during BCT. Many actually contact the back up university and explain the scenario, most dets get it and will allow you to hold that spot a little longer than the avg student. That is the plan B for the stage of an appointee. For others, plan B also includes the case of not getting an apptmt, but you already have that parameter filled. Your plan B now should be to move forward, try not to get injured and keep your fingers crossed that they will make it through BCT without a turn back. The scholarship part is now a non-issue.
It has been several yrs since our DS went through this, but if my memory serves correctly, if you do not respond yeah or nay by that due date, the offer of the scholarship is immediately withdrawn...check the fine print.