Given the scale of this pandemic, it is possible that 2020 is just the first (and worst) year of an annual coronavirus outbreak, similar to how we have an annual flu season.
Coronavirus mutates at a faster rate than influenza (Nextstrain was researching flu when the pandemic started and they are currently tracking mutations in SARS-CoV-2 too). By the time billions of people have been infected, SARS-CoV-2 (the novel coronavirus) may have mutated into a few distinct strains, different enough to each require its own vaccine.
It is also possible that a strain appears that is far less lethal. If this disease was killing 1 in 10,000 instead of 1–5 in 100, we probably wouldn’t even have noticed it until tens of millions had been infected and we’d probably just let it run its course without any actions, just as we do every year with the other coronaviruses that cause the common cold.