What will replace Flash Player?

The plan is that the people who make the games rewrite them to use something else. That's why Adobe have given several years' notice. There is no Plan B.

Well, not only games, but complex RIA applications that still cannot be easily converted or simply impossible to convert, developed by corporations, governments, companies etc.. I think it's wise from Adobe to make the web developers community to forget Flash since it has be so crudely hated (wrongly). The good news is in digital world there is always a solution to bridge, transform or recreate the environment. So for sure some developer teams will find a genius way to let Actionscript developers to continue to develop with their favorite environment and for better performance.