You're right that if the U.S. stopped sending weapons and money today, Israel would not literally collapse tomorrow. The point is that Israel cannot do its genocide and attack its neighbors without constant U.S. support. They'd be forced to the bargaining table within weeks. If Israel was too stubborn to bargain or its victims were uninterested in negotiations after watching a genocide right in front of them, Israel would lose on the battlefield.

The collapse wouldn't happen literally overnight, but it'd be soon and inevitable.