Never mind someone in another space shared with me the answer to this that cannot so easily be found here within learn.microsoft.com. The answer in short is that there is no current plan to deprecate the DATETIME and GETDATE() features and they will of course only create a Backwards Incompatibility for compelling reasons. Such as, the compelling reasons for the numerous deprecations introduced in SQL Server 2017. So with DATETIME no longer an ANSI/ISO Standard which effects its accompanying function GETDATE() the question is, how long before there becomes a compelling reason.
That said be proactive not reactive start the slow migration away from DATETIME towards DATETIME2 and a slow migration away from GETDATE() in favor of the newer SYSDATETIME() function. The other options is to feel the pain when the world passes you by and you are finally forced to make a sweeping major change that just might put you out of business.