From TvGuide

So we've been hearing a lot about Michael's return to Lost. But what about Waaaaaaalt? — Karen
MICKEY: We asked Harold Perrineau if the rumor of a Michael-Walt reunion was true. "It is not true as of this moment," he told us. Another source, though, says that since young Malcolm David Kelley is, like, 7 feet tall now, producers are going to have to explain Walt's fate through others' stories. Remember that kid who just showed up in the clearing last week?


source: TvGuide