My company is still stuck using CVS because when a new project starts up, they want to use the people who are already locked into the old tech and so they end up going with what people already know. Even teams that started with git have downgraded to CVS once the managers starting looking for ways reuse resources.
I'm not saying all companies will end up doing that, but some certainly will (and already do). They may not be vocal about it, though, because they don't want to piss Oracle.
Enterprise IT is broken enough that those multiple system replacement projects were going to happen anyway because of accumulated technical debt and broken development and maintenance processes, and replacing a backend DB as part of that replacement is a rounding error in expense. Sure, it takes a lot of time for the transition to be complete, but lots of those transitions off Oracle are already underway.
More realistically, it's department politics that are going to prevent any sort of migration.
Past performance is no guarantee for the future. We zillions of PC manufacturers before we got the likes of HP and Dell, and twenty years later, we still have them. On the desktop OS/application front, the same happened with Microsoft becoming the main player.
The common theme, I think, is that things are chaotic while there is room for everyone to grow, but get more predictable once the entire pie has been divided (aside: that's an argument in favor of Uber's "land grab at any cost" strategy)
Oracle, Google, or Facebook may eventually disappear, but it won't happen at he time scale at which Altavista or MySpace did.
https://gigaom.com/report/sector-roadmap-cloud-analytic-data...
Whilst Oracle has done absolutely nothing the last few years other than crappy, me-too products they do have a LOT of luck on their side. Why ? Because nobody is touching the EDW (enterprise data warehouse) space. There are no new startups. No disruptors. Nothing. All of the excitement and growth is happening in the analytics space where companies are just sucking all the data from the EDW into Hadoop. And then doing feature extraction, modelling, machine learning etc there rather than doing it in the database.
So nobody is really going after Oracle/Teradata/SAP etc core business any more. It's just kind of forgotten arguably like Windows or Office.