Hmmm...I do not know if I get your point - I ask your pardon, English isn't my native language

! But as I understand it:
Yeah of course, this team rises and falls with the health of all of their three superstars (KG, Allen, Pierce) not only because their individual game will benefit from each other, but mainly because - Posey to, House fro - their bench still is awfully thin and they won't be able to contend for anything but the golden pineapple if one of the three goes down for a longer time.
But actually...doesn't every team playing veterans has the same problem? The more wear and tear a player has the more likely he will suffer an injury...but injuries are not mandatory to happen, just because one player was injured earlier in his carreer. All a team can do is trying to reduce the chance of a serious, season ending injury to a player as much as possible and I think Boston did as good of a job as they could have doing this. The injury bug can bite younger players without a history of injuries and ruin their team's chances of a successful season as well (see Elton Brand with the Clippers).
I don't think that, because of all the factors I mentioned above, one of the Big Three will suffer such a serious injury...or at least not one that is clearly because of earlier injuries (of which I believe the most to be faked or exaggerated, anyways), but because of sheer bad luck.