First you need to decide if the knife means enough to you and that the cost of the knife justifies a custom made sheath. If it is a true custom or fully hand made knife, then yes, it probably does deserve a custom hand made sheath. If it is a Mid-tech and relatively inexpensive compared to one of Mike's hand made knives then you might pause and think about it. I have made many sheaths which effectively doubled or more, the value/cost of the knife, but in each case the knife meant more to the owner than the extra cost of a sheath that they really liked. In the final analysis, it's up to you.............What do you think of your knife and how unhappy are you with that sheath?
Paul