What happens if the database node's network fails just after commit and before responding to the client I know the transaction will be rolled back if connection breaks before commiting.
But what if the commit operation reached the sql server and before it could respond to the client, the network breaks?

The transaction is committed on the sql server, how can the client then know if the transaction was committed or not?
The simple answer is, that a transaction is committed after responding to the client. And it's the client that's sending the commit, the server doesn't decide on its own, when a transaction is finished. (I'm having a hard time finding reliable sources for this, I must admit, but you have my word. It makes sense)  

I tested something similar after it wasn't clear to me when a statement is written to the slow-query-log (the manual isn't clear about this). For this I throtteled my network bandwidth in Linux with netem. The result was, that the statement duration in the slow-query-log includes the time until the result is transmitted to the client.
Feel free to do a similar test :)