There are many things that can be done to reverse the damage LAWA has done at ONT. Not all of those things involve passenger flights.
The Ontario International Airport Authority (OIAA) created a strategic business plan as part of the campaign to take control of the airport. The executive summary is still available on their website:
http://setontariofree.com/
One of their key goals is to Develop Airport-Related Businesses. The area around ONT is already home to large warehouses, logistics centers, and freight transportation companies. (That's one reason why ONT doesn't have curfews like other So Cal airports.) Improving cargo facilities and streamlining processes could result in significant revenue. Additionally, OIAA also wants to "Re-initiate negotiations abandoned by LAWA with potential cargo and other developers".