If it's linked to your account it will be fully functional, but only when it's connected to your home network. There's no way I know of to prevent using the mechanical reset button to do a factory reset, and once that's been done it can be set up from scratch to be used on a different account.
I don't know if there is anything Roku can do from their end if you supply them with your account information, model and serial number. You could send a private message to @RokuDanny-R to find out. Click on his name to bring up his profile, then click the purple "Sent this user a private message" button.
Roku Streaming Stick +, 3810X, Ser YH0059427035, wifi - Samsung UN55ES6100
Roku Streaming Stick, 3600X, Ser 5S56D8240827, wifi - JVC EM37T