I don't think Thurston will leave the cowboys. The cowboys are about to offer him a huge contract with third party sponsorships worth 700k per season, which will price every other club out.
http://www.news.com.au/heraldsun/sport/nrl/story/0,27074,25794124-14823,00.html
http://www.news.com.au/heraldsun/sport/nrl/story/0,27074,25794124-14823,00.html