You can leave it for now - unless you can't use it at all anymore with out buying it, then I'd go ahead and uninstall it.
And if your hard drive might be getting full then go ahead and remove it, if you change your mind later on , you can always go to MS and download it again.
The files you made with MS office should be saved in your My Documents folder- so removing MS office program won't delete any of your personal files.