The legacy of SOFIA and perspectives on the far-infrared

On 29th September 2022, the airborne observatory SOFIA flew its final science flight, concluding nearly 12 years of successful science operations. While the Astro2020 review has enabled the possibility of a NASA far-IR probe mission, such a platform - if realized instead of the alternative X-ray option - would likely not observe at best until the early-2030s. Therefore, for at least the next decade, the wavelength regime between ~30-300 µm has become inaccessible to the international community, aside from an assortment of upcoming and planned balloon-borne missions. This regime encompasses a range of key astrophysical observables across multiple spatial scales - from local star-forming cores, to molecular cloud complexes, to entire galaxies. As demonstrated by SOFIA observations, these include tracers of star formation however, the lack of complementary access to the far-IR will hamper our understanding of key concepts. In this paper, we will overview some of SOFIA's science highlights, and present a number of major science cases for continuing far-IR observations. We will outline ongoing efforts to reprocess and preserve SOFIA's scientific and technical archive. Finally, we will discuss how SOFIA's scientific legacy was enabled by particular instrumentation & platform capabilities, establish where and how these capabilities can be improved upon, and place these in the context of future airborne and spaceborne far-IR mission proposals and concepts.