There is definitely the potential to cause other parts to no longer work if the index page is used for anything other than the links, but as far as I know the main index page in your site should just be linked to and not have any real functionality on it itself.
You should make a backup of the files before you do this then test out the site by trying to login from the index page then try to go from the index page to other pages in the site. If everything seems ok then I think this would be a good alternative.