Is there a plan to retain zip version download of codeigniter4 without composer ?

Yes, there will be a downloadable zip for CodeIgniter 4. There will also be a composer download.

Composer is being integrated in the sense of supporting the composer autoloaders mechanism, in addition to the CI4 loader and classmap.

Composer is one of the tools that should be in a developer's toolbox, IMHO. It doesn't solve all of your problems, but is very handy managing dependencies on other packages or components.