If my current job offered me another position due to closure but I decline and work someplace else will I still gain the severance.

In the U.S., that is completely up to the company since there is no legal requirement to provide severance pay (and my guess is that they will consider you a voluntary quit and not extend the severance package to you).

Ok that's kind of what I thought but the position is sales and my previous job was operations management.

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maybr but probably not. It up to the company