If everyone had their heads screwed on properly (though that is far from guaranteed) when the order was drafted and signed then it will have been a capture order, the political consequences would and will be severe as all those who support the jihad against the West now have a very public rallying cry, especially as, from their perspective, it is easy to spin these events as America sending black-ops assassins.
Now as Nuclear1 said when instigating operations against armed opponents it is impossible to account for all the variables, all osama's bodyguards had to do was wear gas masks and stab vests to bring about a situation where only flash-bangs are going to be effective as an incapacitation device. Also should the entry team not identify Osama amongst said bodyguards during a shoot out with them and you could easily end up killing him without realizing. There is a lot that can go wrong during these sorts of ops and training + equipment can only improve an op's chance of success not guarantee it
As for the morality of military raids like this one which is the greater evil, allowing Osama to carry on being a figurehead for the jihad or breaching a nations sovereignty for a few hours in an attempt to capture Osama for trial?
neither option is faultless but personally i prefer the latter
Flash bang grenades?
If Osama was captured, would it be worth the effort, or it's really not much better than killing him?
FB's are not perfect, also you have to get the grenade behind any cover the bad guys are using and throwing accurately is not easy with bursts of weapons fire flying at you. you have to throw either from behind you cover so cant see where you are throwing it and visual memory is not perfect in itself, or to see the target as you throw it requires exposing yourself and your vital and only lightly protected head to said weapons fire which if the body guards have any reasonable level of training will be fairly accurate
