The problem is not that it's finite, the problem is that by the time prices rise enough to discourage people from using it frivolously, you might already be dangerously low on it.
This is a really interesting question. Is it? My intuition would say no since you have no inherent duty to protect or help others. I have no clue though.
If there's no downside to leaving the ladder in place, then I would think yes - there's a reasonable expectation that people will die due to your actions. You'd likely have to argue about "involuntary manslaughter" vs something more intentional though, depending on circumstances.
If there is a reasonable downside, probably no? You have a right to try to keep yourself alive, in nearly all contexts.
There are alternatives to oil for energy, a lot of them. Helium is unique in its place in the universe, for the properties it possesses as an element. And once it's gone, it's gone. Hydrogen is similar but extremely volatile, where Helium is not volatile.
Helium could be made with nuclear fusion, but a 1 Gigawatt nuclear fusion plant would only produce 200kg of helium per year, so it's still not a viable path to make the quantities of helium we currently use. Current usage is almost 30 Million kg per year.
The problem is not that it's finite, the problem is that by the time prices rise enough to discourage people from using it frivolously, you might already be dangerously low on it.