If you want to sell it and then buy a new one, do that.
If you’ve enjoyed it for a month and felt satisfied with the purchase until something new came out, then I don’t feel it’s appropriate to return it like it was a free rental. Your Steam Deck didn’t get any less good just because a new one came out.
WoW is definitely playable on Deck’s power, though not on the highest settings by any means (probably more medium to low) and probably moreso in the 30fps range rather than 60fps.
I would not recommend trying to raid on a controller though. I have messed around with WoW on controller since they released support for it, and while it is fun, it is too difficult to even have enough keys to bind to much less maneuver and aim what you need to aim imo to be the preferred way to play. Definitely have a docking station and a keyboard, or a bluetooth keyboard. The UI/chatbox will be hard to read on the normal screen if you’re not holding it up to your face, so most likely if docked you’d want a monitor too.
I think for WoW, a laptop or gaming PC would probably get you farther in performance in that price range. I have a laptop I bought in 2012 for $1400 that I can play comfortably on medium to high at 60fps even in new zones. But if there are other things that draw you to the Deck, the Deck itself is a really cool and fun piece of tech (ex. traveling, other controller based games you do enjoy, wanting to practice using Linux, etc).