On a more serious note, the silver denarius actually holds up pretty well today. It has about $2-5 worth of silver in it, and originally had a nominal value of $20-50 (depending on how you calculate it, not debasement). If you're collecting them today, you can get some of the cheaper coins for $20 or so.

I'm no historian, but I'd wager the denarius never collapsed the way - say - the Confederate dollar did. It probably just became rarer and rarer in circulation as old coins were melted down to mint new ones, and then one day it was worth more as a store of historicity than value