Pretty Much what TMC said, I think that he can perform FTG (60% positive thats why he was holding the FTG Kunai in his mouth even after Sasuke had just got sent to him, the other 40% being that he had it so Minato could come back later), and that after he woke up, he marked Sakura with the FTG seal. After all, it has been pretty obvious for some time now that Madara wanted Obito's eye, even Naruto could pick up on that. Since he has godly sensory skills now, and knows Madara's motive, he probably will notice Madara's absence or FTG to Obito's dimension.
Either that or he might have hidden a clone in the other dimension, which is also reasonable.
Not true, FTG never goes away.