A lot of businesses have collapsed when their core expert(s) left.
Most medium-sized and small business units have many employees who are extremely difficult to replace, and a few groups who simply cannot be replaced quickly enough to save their projects.
If those projects are a significant proportion of revenue, the business often fails.
While no one person should be irreplaceable, groups often are.
Changes to company policy - esp. dress code - are often the most effective way of alienating a group. Especially when the group is close-knit and highly effective.