Assuming this is true, (which, in the Middle-East, is a big assumption), this is very interesting, I can't imagine that the regime in Iran would want him in their country, unless he stays quiet, which is unlikely. Bad news for them might be good news for us: an opportunity to clean house on his faction while he is somewhat out of pocket; it reinforces our case that the Iranian mullahs are up to their meddling necks in supporting rebels; and, it gives us another excuse (because we're stupid enough to need one) to pinch the Iranians. In any case, we must make sure, at the very least, that he cannot come back.
From al-Sadr's point of view, I think this is a bad move. Yes, there's about to be an American crackdown, but our idiots of Democrats are going to see that the US troops leave soon, or at least cut back the tempo of operations, which would leave al-Sadr's organization, (the best organized of any of the Shiite factions), in the catbird seat.
Hiding and waiting the Americans out seems at least worth considering. Fleeing to Iran makes it harder to maintain personal ascendancy over his organization -- hard to enforce discipline on your followers from a distance, much less eliminate local rivals -- and also makes him subject to the vagaries of Iranian politics. And just think of all the fun we can have with propaganda painting him as an Iranian stooge.
I will have more to say on all this, I hope, later.