Dawn Ostroff wanted to cancel Supernatural at the end of season two, yes. She wanted to focus on the Gossip Girls and Melrose Place 2.0s of the network. The studio execs at Warner actually intervened, because SPN brings in a shitload of revenue from overseas markets for the studio. Warners owns half the CW. Ergo, the reprieve, but Kripke acknowledged that they wrote the season two finale that way for a reason.