The exact WLAN range of the Tobii Pro Glasses 2 depends on the hardware you use and the environment you are using it in.
Outside of buildings and in environments with low radio pollution you will have a wider WLAN range than inside of buildings and in environments with high radio pollution.
In case the Tobii Pro Glasses 2 went out of range, they will disconnect from the PC/tablet. However, if the Windows feature for automatic re-connect is enabled they re-connect automatically when back in range. To enable the automatic re-connect feature make sure you select the option "connect automatically" when configuring the WLAN connection the first time. In case you already configured a connection for the Tobii Pro Glasses 2 you can disconnect from a previous WLAN network and let Windows "forget" the WLAN settings. Then connect the Glasses 2 via WLAN and choose "connect automatically".