Your "solution" does not work well with people on mobile. People on 2G/3G/LTE can alternate rapidly between online and offline. This kind of problem is easily s

Your "solution" does not work well with people on mobile. People on 2G/3G/LTE can alternate rapidly between online and offline. This kind of problem is easily solved by the chat server behaving like a store-and-forward device. Which is exactly what email is. But nobody likes to converse entirely using emails. Chats have an important place because they allow us to say small things, quickly. What you suggest will result in no viable chat for mobiles, only emails. We can probably make a chat app that looks and feels like whatsapp but actually sends an email for every message. Dunno what problems this might have.