if you disable the news feature with this patch, how does one edit the contents of the "Main" window? Shouldn't that also be hidden?

Disabling the news feature hides any news in the database from the main page. In that case, the main page is almost useless and hence the default home page should be set to point to my view page (if that is not already the case for you).

$g_default_home_page = 'my_view_page.php';

If you want to continue to use the news feature in MantisBT, then you should re-enable the news feature in your config_inc.php:

$g_news_enabled = ON;