Spacecraft n a suicide run at full speed verus Imperial palace I'm putting my money on the ship winning. And with Palpatine's arrogance post ROTS he'll never see it coming because he believes he is invincible
The planet shield would prevent anything coming from space, and there is certainly a huge no-fly zone around his Estate/Palace/Centre of Government.
His own building is also most likely shielded, reinforced. There is a cortosis layer around his private appartments. The Imperial Guard is on duty 24/7.
No sir. A group of rag-tag terrorists couldnt just beeline at the Emperor to kill him. Because he also has the Force, which even furtgere protects him.