I found a great resource that will interest you. It's an online tool that assesses the sustainability of your program, and it's free. Invest 15 minutes of your time and you'll get a report that tells you where to focus your energy.
It's the Program Sustainability Assessment Tool, developed by researchers at Washington University in St. Louis. They've got a Sustainability Framework that is well-researched. It stands on eight pillars – stable funding, strategic planning, and partnering, among others. They've even tested the reliability!
Check it out. Touch base and let me know if you might track your program in this way.