They don’t really answer that question in this commercial, but the vague response seems to be this: Terrible things would happen, that’s what! OMG OMG WTF Be afraid!
This idea of the Christian God being like an abusive stepdad who threatens to kill his family if they don’t buy him a nice tie for Father’s Day definitely has its biblical basis. Some of the more modern Christians try to frame this as if God’s usually protecting us, and that when horrible things happen that’s just the physical world attacking us for being sinful and it happens as a result of God’s inaction. But then there’s Isaiah 45:7:
I form the light, and create darkness: I make peace, and create evil: I the LORD do all these things.
I still don’t get why people who believe in gods never seem to consider the possibility that God’s as petulant and childish as he appears to be in the Bible. If a real person made these kinds of threats, they’d probably be locked away. But when it’s an imaginary deity, suddenly they deserve worship. It makes no sense at all.
That last sentence was brought to you by Captain Obvious.