I would rate the likelihood of a coaster brake failing as extremely unlikely. I volunteer at a non-profit and have overhauled hundreds of coaster break hubs. Even the cheapest hubs on the lowest end Walmart bikes have very robust builds. They are the one item on BSOs that actually have enough grease.
The most likely ways to damage a CB hub are to burn off the grease by riding in very hilly areas (riding a coaster brake in hilly areas doesn’t sound fun in the first place) and forgetting to connect the reaction arm which would loosen the hub during braking and lead to bearing damage.
Last edited by aggiegrads; 05-25-21 at 07:02 AM.