I think they mean unavoidable from the company's point of view - they can't make you quit, so when they hire you, they have to assume if they ever need to lay you off, they'll need to afford your severance.
Yes — I was slightly incomplete in my description, but you are exactly correct about what I meant. Company liabilities include things you are obligated to pay under uncertain future circumstances, so accountants have to make sure that such liabilities can be handled if they ever arise.
