I say yes. Never has she been in a better position to do so: Her health is good, her attitude is positive, and she is playing tennis out of her mind.
She does have competition: Maria Sharapova just showed that she is definitely back in a big way. Serena Williams, if she is healthy (a big "if") is always a threat, and I'm not ruling out Lindsay Davenport to take one of the big four in 2008. Other obvious competitors are Jelena Jankovic (if she can figure out a way to beat Henin), Ana Ivanovic, and a healthy Amelie Mauresmo, Henin's rival. Or someone else could step forward and become a threat. But conditions are such, at this time, that Henin is poised to win all four majors. She doesn't really have a "bad" surface, though grass is obviously the toughest for her. Her main competitors--Sharapova, Williams and Mauresmo--have all been set back by injury or illness. Venus Williams likes to win Wimbledon now and then, but Henin can probably handle her.
There is no doubt in my mind that--barring illness or injury--Henin will win a couple of Slams next year. And under the right conditions--or maybe not under them--she could just take the whole thing.