Immunity will presumably last at least a few months, and the problem always reaches its greatest severity in the winter months because people are indoors more. We will just default to the influenza model, where there are circulating betacoronaviruses every season and we try to predict and vaccinate against them. The Middle East deals on and off with MERS.
Presumably immunity goes away once the antibodies are gone, but does the body remember the virus for next time? Assuming the virus does not mutate too much from year to year, at what point will it not be novel anymore to the human body? Will subsequent infections be easier for the body to fight?
From what I understand you build some resistance as you are exposed to multiple variants of the same flu virus so it's quite possible this would hold for coronavirus making refection less likely to lead to a severe infection.
Lets also not forget that there is likely to be well studied effective anti-virals at some point like we have for the flu today.
