Without Alexander, the expedition is off. Macedon, known for its messy successions, descends into civil war. Whichever general can get most of the army behind him wins. Parmenion, Antipatros and Krateros all have a good shot. Alexander's younger hand-picked officers haven't had a chance to prove themselves, and probably wouldn't be able to rally the needed support, regardless of their talents. Observe that Alexander just emptied the entire treasury to finance his expedition. Macedon is broke, and that's not considering the efffects of a violent succession war. Whoever wins is thus in a bit of trouble, no matter what.
Holding Greece will be difficult, since they were eager to rise up when (they believed) Alexander was dead in OTL. When he really died in OTL, Alexander left behind a vast empire with a full treasury, so this didn't work out for Greece. But this earlier death gives Greece a far better shot against a bankrupt, in-fighting Macedon.