The key to “sustainability” (which, as previously written, is not “survival”) is proof that your particular arts charity is achieving specific community goals.
Each social service and social justice charity measures its results toward the execution of their mission. Those results have a direct link to funding and community support. Your arts charity, then, must find results that apply specifically to your organization.
Charitable results cannot be measured by paid attendance or positive economic impact. Those are commercial results and byproducts — data used by sports teams to get cities to build them stadiums or by entertainment conglomerates to allow regions to let them build casinos.
So what makes your arts charity charitable? Answer that and you’re 99% there.