Since this is yourbailiwick, Zheng...let us assume that Malaya is stretched into late spring, rather than mid-February. Let's assume - it seems fairly safe to assume - that the IJN still acts to dispose of ABDACOM naval forces in the Java Sea with reasonable dispatch, regardless of whether the amphibious attack on Java is delayed. After all, Yamamoto will want to minimize the prospects for reinforcement of Singapore by sea, if nothing else, right?
Is the Darwin Raid still on the table? What does Yamamoto most likely do with the Kido Butai if Operation C (the Indian Ocean Raid) is off the table? Does it get used merely for naval support for Yamashita? Sent back to Japan for refit? Something else?
I'll give you the ultimate non-answer - IT ALL DEPENDS.
Seriously though, it really does. The Darwin raid will still go off at some point, maybe not the same dates, because the Allies are running convoys to the DEI from Darwin. In fact, in a TL where the Allies are doing better, Darwin may even get more tender loving care from the Japanese.
I have no doubt the KB will get involved heavily. I agree that OP C as we know will not happen but I assume in this TL that ABDA naval forces are making some sort of nuisance of themselves and the KB will be called upon at some point to help deal with them, especially if Force Z is still active in some way shape or form.
The other two big questions are when and where does the Eastern Fleet start assembling? Probably not on the exact same timeline as OTL but there will likely be some sort of RN naval buildup in the Indian Ocean and if they are operating further forward to support Allied operations in Malaya and/or the DEI I imagine Nagumo will try to bring about an engagement at some point. The other question is what happens when the US Pacific Fleet's activities reach a sufficient level of annoying (Tokyo Raid or something else) that the Japanese decide they have to be dealt with. What happens when the KB and other major units are pulled out of South East Asia to go after the Americans when there is still unfinished business down there?
Essentially you are now in a totally alternate TL and things are going to be very different.