If you do want to delete your Linux partition and return that space for use with Windows...Yes I think you can just delete them via Windows disk management utilities, though there may be some task you need to do for the boot manager...I've actually never done that.

About Proton: You will be using Proton to game in Linux Mint; it's not another operating system.

Proton is a compatibility layer written by Valve that allows Linux to play Windows games. If my understanding is correct, it's a modified version of WINE that also translates Microsoft DirectX API calls to Vulkan calls on the fly so that the Linux kernel can understand them. This opens up almost every game in Steam's catalog to Linux users. Some online competitive games intentionally still don't work with Linux mostly because Anticheat on Linux is a whole other ball game.

Proton comes with Steam. You install Steam, you've got Proton.