From what I've read, given the difficulty, subtly and complexity of their task, that's very much the sort of thing they worry about. Maybe not on that scale.
Inside the James Webb Space Telescope's control room -- Phys.Org [phys.org]

From the link

Whitman [RichCC: Rusty Whitman, Flight Operations System Engineering Manager at Space Telescope Science Institute] is still worried about what could go wrong: "I'm nervous about the possibility that we forgot something. I'm always trying to think 'what did we forget?"

The lens cap lol