1. How does a multi-billion dollar company just disappear in three years? Sure, the CEO disappears, but, it's not like everyone just looks at each other and go, "Well, I guess that's it then, I guess I'll go work for Starbucks." The company itself has assets, at the very least, wouldn't someone swoop in and take it over? It's a mystery I don't think they will go into, and I think it was done for aesthetic reasons.
As per Elseworlds part 2...
Oliver: "Apparently, after he left, Bruce's board of directors went to town with a bunch of aggressive get-rich-quick deals."
Also in Elseworlds, Kate says that she's in the process of turning the Wayne building into a real estate development firm.