Don't leave it hun. I'd say it has died, and now has an abcess. The reason it's not hurting is because the infection has somewhere to go, ie. has formed a lump, rather than sitting (painfully)in the bone. I would say that it's pretty definite you will need RCT or the tooth extracted. The reason he's suggested an xray now is see if there's infection present (der) and where it is.

I would suggest going for the temporary filling over the extraction. They can use materials that are sedative, which might just stop the tooth from becoming sore. The problem with just doing the filling is that you run the risk of the tooth becoming very painful. But really, the best course of action would be to have the first stage of the RCT done, where they open the tooth, remove the dead nerve, and put a dressing inside the tooth, with a temporary filling over the top. This should then keep you comfortable until your baby is born, and then you can have the rest of it completed.

Oh, and it is safe to have LA during pg, just make sure your dentist knows that you are so they use the right one.