"Once the trial period expires, you will have the option to purchase an Office 365 subscription or reinstall your current version using your original product key." You will stay on the Office 2016 Preview track until you uninstall the Office 2016 Preview or until Office 2016 is released."
"This will install the Office 2016 Preview on your device. Microsoft describes both scenarios as such: Make note of the product key on this page, you'll need it to authenticate your install.As above, Microsoft recommends the 32-bit version by default.