To see all disabled saved searches, i.e. alerts & reports, use the "All configurations" listing which you can find under "Settings". App context "Search & Reporting (search)" and search for "savedsearch" or use this link:
You cannot. At least, not in a way that your installation will continue to be supported by Splunk support. The 'alerts' page at http://localhost:8000/en-US/app/search/alerts is not a standard XML or HTML dashboard. It is based on core Backbone.js routers and views and is in a part of the overall Splunk web UI that is not intended to be user modified.
If you are willing to dive deep into the internals of the Splunk UI, put your support in jeopardy, and do things that will be replaced every time you patch you can start to look in $SPLUNK_HOME/share/splunk/search_mrsparkle/exposed/js/views/alerts/table/Master.js and see how the page is assembled. I wouldn't recommend it though, especially not for production. You're kinda on your own there.
There's two things I hear here that could be reasonable ERs -
Adding the enabled/disabled status as a header column to the alerts view
Exposing the ability to customize fully the columns and data shown in pages like the alert view (and other manager pages built with the same approaches)
I would suggest you submit an Enhancement request for it. In the meanwhile you can use the | rest command to build a dashboard of enabled alerts which may suit your purpose partially.