RWI is an internal inhibit. It is not controlled by WE/. During RWI, condition of WE/ pin or any other control pin has no relevance. And hence, data cannot be corrupted by any means during RWI. Only at the end of the RWI, the WE/ condition will matter. Therefore, we suggest a pull up on WE/ pin to ensure that unwanted writes do not happen after RWI is enabled (and the controller is still booting up).
Note: To state the obvious, the pull up helps only if the controller IO is in tristate when nvSRAM has completed boot up - at end of tHRECALL - and not if it is in LOW state. Also, you can see that instead of WE/ you can ensure CE/ is HIGH which would have the same effect since any unintended write can happen only if both CE/ and WE/ see a LOW condition at the pins.