BuddyPress.org

The hosting guys could change it, but are unlikely to change it. Although usually they give priority something like this:

index.htm

index.html

default.htm

default.html

index.php

So, it will search for the files in that order.

Long term though, you should likely just create a child template for your blog so that it will go to your blog’s home page. You can make it look just like your index.html page (or at least really close).