ORIGINAL: poodlebrain
What morale and experience levels do your defenders have at Langsa and Sabang? What sort of leaders do you have? These might be difference makers between holding out for 40 days and 90 days.
The US Army divisions have decent experience, low fatigue, good morale and excellent leaders. There are four divisions - Americal (currently broken into RCT), 27th, 32 and 36th (the latter two numbers going from memory).
There is 1st US Marines with Archer Vandergrift in command. An excellent unit with '43 squads now, though really badly roughed up in earlier combat. AV is back to about 250 now.
There is an Indian unit of decent experience and good leadership.
There is 18th UK Division, but it was divided up to help garrison various islands and is now pretty weak.
Right now, I think John has at least six divisions committed in Sumatra with at least two more inbound and perhaps four to six up in Burma. I think with good terrain and supply and good prep, the Allies might tie up a fair number of enemy divisions in Sumatra for a long time to come. If the enemy troops are badly disrupted in amphibious landings, all the better.