Who is asking? Generally as a small software company founder, key man risk worries come from middle managers who are afraid of the worst case (you dying or something) then their boss asking, so they are just trying to cover all their bases. It should be a minor consideration for the overall business who is the ultimate customer (as there is risk in everything - getting acquired, going bankrupt etc.), ask their concerns and reassure, focus on the value and product since you have a niche