If Oracle goes down, a lot of businesses are going to be in a lot of trouble, and there will be a lot of fighting over the scraps.
Regarding Java, SAP has long switched over to openjdk (though oracle java is supported in some cases). Specifically, they have their own custom fork of openjdk "SapMachine" precisely to be independent from oracle (FYI: if you look at openjdk upstream you will see many core contributors are employed by SAP)
In general, I would say that the actual tech companies that have to interact with oracle's stuff are generally very well equipped to drop them or have already done so. The bigger issue are legacy "consumers" of oracle (e.g. if Pepsi has their data in oracle DB), which often do not have such contingencies.