People laugh, but if these people are good at sales their skills are very transferable. More than likely they will find some other industry and while it might take six monhts to a year to build up a client base the more determined ones will be selling something different. You sort of have to accept that this is going to happen if you are in sales.
I personally try to use a 4 year average so any great year is forwar averaged so that I can not only control spending but simultaneously ahve a solid reserve to fall back on. I don’t think that this is unusual.