If you send a bird in and it tests positive for HPAI they’ll more than likely euthanize your whole flock. If it is bird flu you may lose them anyway to the disease or there could be survivors, but that’s up to you what course of action you want to take.
Standard procedure is depopulation of a flock that tests positive to limit the spread of bird flu. This method used to be very effective, however bird flu is now almost everywhere so that method of control isn’t really effective anymore, however limiting its spread should still be taken seriously.
If you decide against necropsy I strongly advice quarantining your flock so that if it is bird flu it doesn’t spread beyond your flock and not going anywhere near anyone else’s flock, do not go near any zoos or farms, parks, anywhere you could bring the disease yourself.