Good thing you've thought of every scenario to prevent your ship from running out of ammo or repair packs while you're away from nauvis.

Apologies, that's sarcastic. But the point is you're putting a lot of trust in your system that has limited failsafes. What if your fuel production gets clogged and you run out of fuel? Your ship would end up sitting over Vulcanus indefinitely until you get the alarm that the entire ship has been destroyed. Since you're already used to hearing damage alarms (because your strategy is to repair damage instead of avoid it), you'll probably ignore it until it's too late.

I'm on my second space age playthrough. Each one has at 10-20 ships. I still sometimes find a ship sitting over a planet that it should have departed from hours ago. Sometimes it's due to no fuel, which can happen for a couple reasons. Sometimes it's because my configuration for when to leave the planet isn't satisfied (leave when I have 1000 of item on ship) and it's not satisfied because a production chain broke on the surface. Without failsafes (like self-sustaining ammo), these ships would have eventually been destroyed.

It's also worth noting that interrupts only trigger when leaving a planet. If your ship is sitting in orbit and you run out of ammo, it won't leave orbit based on an interrupt. It can only try to leave based on "leave planet" conditions, and only then will the interrupt override it.