Weather considerations
I delved a little into this in order to get some feeling for possible wind and current drifts. I found the closest stations to be Kuala Terengganu (WMKN) in Malaysia and Phu Quoc (VVPQ) in Vietnam, on both sides of the Gulf of Thailand.
During the last two days, WMKN metars show weak southerly winds with NE in the afternoons, presumably a coastal seabreeze, less than 10 knots. VVPQ reported slightly more breeze at E-SE between 3 and 12 knots.
It is of course possible that winds in the middle of the gulf, where MH370 vanished, are different, but my guesstimate for the area is for light to medium winds from the E-S sector. Which would have kept any debris from an in-flight breakup in a reasonable area, and pushed any debris and oil on the surface in the direction W-N.
Perhaps someone can dig out some upper level wind charts from the area for the last two days. This might help in guesstimating the debris spread from any in-flight breakup at cruise level.