No need for panic. Not just yet.
With 28% computers still estimated to be running Win7, there's still a long way to go.
Microsoft recently announced there will still be Security Essentials updates. (they're coding them for the large organisations paying for continued Win7 support - so may as well let the general public have them too)
Several independent Anti Virus products for Win7 will also continue to be updated and supported.
Finally, there's the precedent of the XP patches released to address the Wannacry attack in 2017 - years after MS ended XP support, and threatened ongoing doom and gloom.