my brush presets tab has gone missing. I mean the icon that is usually next to the layers tab and the tool options tab. I don't know how to get it back and it was a rather integral part of the program. Please help!

you can re-activate it from the menu: Settings → Dockers → Brush Presets

if your workspace ever gets messed up, you can restore it to one of the built-in workspaces with the button at the top right of krita, or from Window → Workspace. Be aware that all your modifications to docker positions and such will be reverted, unless you save them as a workspace of your own first: Window → Workspace → New Workspace.