This situation came up in last night's game.
A dragon with flyby and grab swoops down, bites the party barbarian (triggering grab), successfully grapples the barbarian in its jaws and begins to fly off, casting quickened invisibility as it does so (to avoid being shot full of arrows by the party zen archer).
The dragon is invisible, but is the barbarian still visible ?
The following turn, since the roll to maintain the grapple is an "attack", the dragon will become visible again ?
If the barbarian is entirely contained within the dragon's closed mouth they will be effectively invisible. Any parts that dangle out are visible. The barbarian is a creature, not gear.
The following turn, since the roll to maintain the grapple is an "attack", the dragon will become visible again ?
Yes.