Windows Server won’t be getting “sold off.” I’m not sure you understand just how entrenched Windows Server is in the Enterprise and just about every Fortune 500 company out there, including huge telecoms and ISPs. MS still makes a ton of money off Server, and most of the companies/Enterprise using Server aren’t even thinking about Azure.
Windows Server gets to exist so long as it acts as a funnel into Azure. Someday it will be sold off to Wipro, a la VMS or OS/2.