I'm sure this has already been mentioned, but, well, with River and everything... if the Doctor died on the beach, but River's either already seen an older version of him (when he 'found out who she really is') OR at the time, he knew everything about her... which it seems he didn't.
So, at the time of the Doctor's death in TIA, River must know he's not really dead, or something like that? If she first met him when he was older, and he died before he became older, then wouldn't that create a paradox, because she wouldn't be there? And since nothing went boom in the universe (or did it?), she must know that somehow, he doesn't really die...
bit of pointless spec there though... ;P