I have a Mervyn's department store card and it was one of the first cards I got when I turned 18, I am now 23. The card has longevity and good payment history. However, all Mervyn's stores have closed in my state so that guarantees I will never use this card ever again. So my question is if it is better to just leave this account open since it is one of my oldest accounts but it would be inactive forever, or close the account altogether?

I believe it is better for your credit score to just leave the account open. My sister and brother in law were applying for a home loan... my brother in law closed an inactive credit account and it instantly dropped his credit score. Took a while to get it back to normal after that. Hope this helps. Blessings.