Splash page to replace current homepage

We’ve made a splash page that is straight html and is sitting in root as index.html.

We can make this page the default root landing page by giving .html preference over .php in .htaccess and this works fine but the splash page contains a link to the previous homepage at index.php and when this is clicked the link reverts to the splash page because .html is taking preference.

What’s the best way to deal with this – i.e:

1) have the splash page sit in root (i.e. not in WP) and replaces the old WP default landing page

2) have a link in this splash page which then links to the old default landing page in WP.

Cheers!