Just because Lance is gone does not mean Zavala will die or has to die. They can just get a new VA
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It's more a matter of respect. Also he had a sort of unique voice so finding someone who sounds like him, would be a tall order. Personally I think whenever a voice actor or actor dies, it's better to do one of the following: kill the character off, have the character leave and replace them with a different character, or in the case of VAs, have the character suffer an accident and lose their voice.