Technically, my understanding is that plastic deformation has already occured if the mast is bent as described. Plastic deformation is defined as a material not returning to its original shape once a load is removed. Elastic deformation occurs when the material returns to its original shape once the load is removed, this happens all the time just through everyday use.

Just from limited experience with aluminium in general and some smaller dinghy masts, small bends that don't have stretch marks can be easily removed with little fear of weakening the mast. Stretch marks indicate that dislocations have occured in the materials crystal structure and I believe that is when fatigue may become an issue, and straightened will be almost impossible anyway.