With it only being the second season of the new CBA rules, it's hard to guess what people will be doing at the trade deadline, but it certainly seemed like teams were a bit more reluctant to give up much for the half season rental players. It certainly isn't going to help anything that Morneau has only played 38 games from September 1st on over the last four years. I think if he is doing well it's going to piss off a lot of season ticket holders (who are already a bit pissed at the team) if they get rid of him for some kids who may or may not pan out. It's not like we're going to be able to get the next Mike Trout or Stephen Strausberg for him.
Last year the Marlins traded two of their top ten prospects for a half season rental of 36 year old Carlos Lee. He had a .747 OPS and hadn't OPS'd above .800 in 3 years. So even with Morneau's injury history I think it's reasonable to believe he'd bring back something of significance at the trade deadline.