After 2 cruises in a Verandah cabin on the Wonder, I can tell you that NO there are not any robes just waiting for you in your cabin.
However... anyone is welcome to go and borrow one from the spa - for free. All you have to do is ask & they will give you one. If you go work out, there will most likely be one waiting for you in the locker of the locker room where you leave your stuff. If not, ask.
After your workout, you are welcome to borrow the robe or (like I did) wear it out to the pool or to your room or wherever.
You just have to remember to leave it in your stateroom to be returned when it is time to go.