Sure, it is handy to have a Josh that miraculously saves your project, but the fact that you needed that Josh in the first place says that you don't have the right staff/skill sets. Needing Josh is a sign to management that there are some serious shortages that need addressing.
Sure, all companies sometimes need firefighting, but the REAL firefighters are those that not just put out fires, but help to prevent there being other fire call outs. Really effective fire-fighters help mentor others and, in essence, make themselves redundant. [Aside, firefighters (of the thermal sort) actually spend a lot of their time doing fire safety inspections etc for this very reason].
Those Joshes that code so cryptically that they are needed forever are essentially blackmailers and saboteurs. They force you into a position where you have to put up with them to keep functioning. Make a plan to dump them and replace them.
I've worked with a few Joshes in my time. The one was brilliant, but it took the next three most productive engineers to clean up after him and quite a few almost as clever people just quit because they could not work with him. When you realised that the cost of having him around was not just his remuneration, but also the opportunity cost of the next three engineers too, then he didn't look as valuable.