I can confirm that this solution is working and the batteries can last more than a year. The batteries for the temperature sensor died 1,5 after the installation, from the other sensors still working. Even if the connection with the Xiaomi servers are lost, the connection with your network still works. You can also connect other sensors, like the water leakage sensors, and every new one that Xiaomi releases.
I will advice you to buy the new Aqara sensors and Gateway (with the square shape) and not the old Mija (round shape), even if the price is more expensive.