Learn Dutch: Een lange levensduur moet hoe dan ook gegarandeerd worden. - A long lifespan must be guaranteed anyway.

The phrase hoe dan ook literally translates to "how then also." When you combine a question word (like hoe, wat, or wie) with dan ook, it creates a phrase meaning "no matter [question word]" or "[question word]-ever." So hoe dan ook means "no matter how," "however," or in this context, "anyway" or "in any case."

Why are the verbs gegarandeerd worden placed at the very end together?

This is a passive sentence combined with the modal verb moet (must). The modal verb takes the second position in the sentence, pushing the rest of the verbs to the end. Since it's passive ("must be guaranteed"), you need the past participle gegarandeerd paired with the passive auxiliary verb worden (to be) stacked at the end of the clause.

Could I place hoe dan ook at the very end of the sentence?

No, that would sound unnatural. In Dutch, adverbial phrases like hoe dan ook belong in the middle of the sentence, which means they come after the conjugated verb (moet) but before the stack of verbs at the end (gegarandeerd worden). You could, however, move it to the very beginning for emphasis: Hoe dan ook moet een lange levensduur gegarandeerd worden.

What is the function of the "s" in levensduur? Is it plural?