The chances of Singapore
I'm not familiar with details on General Bennet, but actually I think it could have had important consequences if Percival had been replaced by a more self-confident general, and that until very late before the OTL fall of Singapore. Percival apparently had lost confidence even before the campaign started, as the British forces present were quite short of fullfilling the strength demand in the plan for defence of Malaya and Singapore (Plan Matador), and it didn't get better from Matador not being initialised at all (ie. occupying the very narrow Isthmus of Kra in S. Thailand, which was the only real acces to Malaya from the East Coast).
I can understand if things looked gloomy seen from Percival after mid December with the Japanese Army having entered the dense roadnet in Western Malaya, that doomed any realistic hopes of stopping the Japanese on the Malayan Peninsula, but I don't understand the passívity in Singapore itself. Singapore wasn't that easy a target to storm, but no field fortifiaction works were undertaken in Singapore. The Engineer officer pleaed for permission to undetake such works, but Percival and the Governor denied such action - the civilians should not be worried (shooting the Governor might be at least at productive)! It is a myth that the guns of the fortress could not cover the land side, most had very good arcs of fire on the land side, but only very few HE shells were supplied. And AP shells, even 15", are not that effective against infantry. Next no serious meassures were undertaken to evacuate Singapore or to build up stores of food and water - i guess it again was the concern about "not worrying the civilans" that counted - but for what purpose if Percival didn't see any hope anyway?
From 10th of December Percival could expect the battle to sooner or later reach Singapore itself, and had he prepared for such a battle/storm I think there is a good chance of the Japanese storm failing. That of course wouldn't necessarily lift the siege, but it would be long time before the Japanese could bring in serious siege equipment and the forces present were already on low supplies (it was quite a job to keep the Japanese forces supplied - the logistic system was already starined to the limit).
Beating back the initial storm would be a tremendous morale booster to the city, it would buy time to bring out civilians and bring in supplies and reinforcements and not at least motivate Churchill to release the neccessary resources for Singapore. He had early in 1941 been recommended by his chiefs of staff to reinforce Malaya and Singapore but refused as he found North Africa and the Med. a more promissing place to find some action. If the need should arise in the Far East "something could always be sent!".
That shows how seriously Churchill underestimated basic logistic laws, but if the siege draws out into March or April there is a real good chance for having something substantial arrive. The forces that the British in OTL had deployed in the IO in late March/early April 42 would alone make a serious difference if Singapore is still on British hands. And if the Japanese have not taken Singapore by April 42 they risk ending like the 6th German Army at Stalingrad. Without Singapore the Japanese presence in South Asia and Pacific is jeopardised.
Regards
Steffen Redbeard