This one is all about opinion, so, take with a grain of salt the size of a house.
You're being a little bit paranoid. SQL Server is one of the most widely used data management platforms on the planet. Depending on the exact measurement, it's 1,2, or 3 in most measures. In short, it's not going anywhere any time soon. And by soon, I'd say, at least a decade, probably more like two. Noises are starting to come out from Microsoft about an update. If we look at the history, 2012, 2014, 2016, 2017, 2019, the progression is pretty clear. It's 2021. I'm guessing they're going to be ramping up a release very shortly.
Also, the fact is, tons of stuff that are possible using the on-premises/VM version of SQL Server just simply are not possible within Azure SQL Database (as much as I love it) or Managed Instances (as much as I don't love it). Organizations who spend money and make Microsoft a profit, want to do those things with the data. So, Microsoft is going to cater to them.
Will the emphasis remain on Azure first? Absolutely. No doubt. It's just too profitable to ignore.
Will things become Azure only? Nope. Not for a very long time. Azure adoption is going to grow. If you don't work with, or have a good knowledge of, Azure now, I'd sure as heck get on that(unless you're only 3-5 years from retirement). However, I'm positive that SQL Server itself is here to stay for the foreseeable future.
But, all opinion. I could most certainly be wrong and will not attempt to die on this hill should anyone disagree.