Shechitah of a Mumar
There was recently a case of a shochet who was found to be secretly frequenting non-kosher restaurants. The intent was to remove him from his position, but since he was considered a respected person in the community, effort was expended to keep the issue quiet. In the interim, he continued to shecht, with his shechitah knife being checked before every shechitah, as is the halachah for a mumar letei’avon (Shulchan Aruch, Yoreh Deiah 2:2).
One day, during this interim period, the bodek of the knife was in a minor car accident and showed up very late. Meanwhile, the shochet in question shechted a few animals that were mixed up with all the other animals. Does this cause all of the animals to be prohibited?
In general, the shechitah of a mumar letei’avon, a person who eats neveilah because he enjoys it, is forbidden, unless the knife is checked. Therefore, in the case you described, all of the animals should be forbidden (Shulchan Aruch, Yoreh Deiah ibid.).
The only possible way I could see to permit this is if there is an instrument for sharpening knives on premises. In a such a case, the Radvaz writes that if the knife had a chazakah of being kosher, then we can permit the shechitah bedieved (Radvaz 1:24, as cited by Pischei Teshuvah 2:3).
However, today there is an additional reason to be lenient. At one time, the knives were made of a metal that was much softer. Today, they are made of iron and dent much less. In addition, this is a question of an issur derabbonon, since the animals of the mumar got mixed up with the animals that were shechted by the kosher shochtim.
Although I am not offering a final ruling on this case until I hear all of the details firsthand from someone involved with this case, the way that you describe it, I would think that there is room to be lenient in a case of major financial loss.