Apachai surviving has no bearing on what will happen to the masters or other "good" characters in the future. Saying the masters can never ever die or lose because Apachai apparently survives (in unknown condition, by the way- he may end up less able bodied in some way, like Ryuto) is like saying no one will die in One Piece because Pell survived in Alabasta. Clearly that wasn't true.
I really don't have a problem with this turn of events. I admit it would have made for some really intense development if Apachai had died, but the fact is that Kenichi will still be shaken by the fact that his master, who seemed invincible before, did come so close to perishing. And he still developed in his fight with Koukin, and the other masters should also realize how high the stakes are despite saving Apachai.
And besides that, any death from here on will have that much more impact, especially if you do start thinking the masters are completely invincible. Not to sound like a broken record, but several people were severely shocked when Ace actually died in One Piece precisely because of this- no one had ever died in the series barring flashbacks, before Ace bit the bullet.