Gaia is such a cool instrument, but I can imagine that it's pretty fragile due to clever elements in its design like using rotation-synchronous time delay integration-- it has to be rotating just right.
From what I've seen, it is actually a simple design, with very few moving parts, which should make it quite robust.
This simplicity is what allows it to be "rotating just right", as it is very close to a rigid body, it is just a matter of applying the right thrust at the right time from cold gas thrusters. There are no gyros, reaction wheels, etc... to take into account.
