Without a doubt, replace it. 500 miles or not, it's just not worth the risk.
Having said that, depending on where the puncture is, you may be able to run on it , cautiously, for a short while.
If it's in the contact patch portion of the tire, replace it immediately!! The last thing you want is a tire to go while you're leaned over. Doesn't matter if you're just riding to the office, or out carving canyons...turns and blow outs don't mix!
A patch/plug is good for getting you back on the road, and into a shop. Use them for what they are designed for...to get you out of a bind... not as a substitute for a solid reliable tire.In the case of a front tire, without a doubt, replace it. You can ride out a rear flat, but a front is nothing worth screwing with.
It's ultimately up to you. Do you think your personal safety is worth the cost of a tire?