Windows 7 will keep working post-January 15. Nothing will change overnight. It is true that Windows 7 will be more vulnerable to attack. That is the expectation. But I don’t think the actual impact will be catastrophic.
For home users that want to cling on for whatever reasons, many of the potential problems could be mitigated using other tools and methods, like VPN, encryption, security software, and a good secure home router.
For many enterprises, they will simply sign up for Windows 7 Extended Security Updates for the next three years of coverage. This covers anything deemed critical or important. Which means not much will change in the attack landscape for enterprises with the Windows 7 Extended Security Updates. Most major apps like Google Chrome browser will also continue to be supported with updates for all users.
For everyone else, an update to Windows 10 or a move to another supported OS should have already happened. A user should never use an unsupported operating system for public facing internet use, like browsing the web or for email. It is bad practice.
For most people, an upgrade should be as simple as a license key. The hardware requirements are fairly low compared to modern hardware. Almost any PC from the last 10 years should be able to support Windows 10. That in itself I would consider incredibly old. Most users are running Windows 7 on more modern hardware simply because they like using Windows 7 and opted to. Windows 10 has been the default OS on a new PC for some time.
If a users’ current hardware does not support Windows 10 or a newer OS, it is likely old hardware that doesn’t support any of the latest versions of apps either. This means not only the OS is out of date, but everything is most likely out of date, which is a much bigger problem.
I’d recommend for those users to buy new hardware.