I think I've posted on the subject of RTB and Steam. Essentially RTB would continue as usual and if certain aspects of RTB are made obsolete by Steam then I'd continue improving the parts that Steam doesn't do so well with regards to Blockland specifically. If Steam replaces all of RTB's functionality really well then I'd just archive all of RTB's files and shut 'er down.
Anyway I've got no intention of shutting RTB down (ignoring what comes of Steam Greenlight), the hosting costs are so insignificant I'll happily keep it running long after I'm gone or offer Badspot the possibility of hosting it himself.