The other answers are (mostly) focused on what the glut of gold would do to the price of gold. However, I think what's missing here is a consideration of the quantity of gold, which can be calculated from the question. The typical modern human body is around 66 liters in volume (according to this source). Medieval era humans might be smaller, armor ect. might make them larger, but this should work for a ballpark. The specific gravity of gold is 19.32 grams per cubic centimeter. Since there are 1000 cubic centimeters in a liter, 1 liter of gold weights 19.32 kg. So the average gold statue will weight about ~1275 kg. Assuming that, as Ruadhan2300's answer points out, you treat the bodies of your own dead with respect and bury them or something, you have as much as 1,275*5,000=6,375,000 kg of gold to work with. This is a lot of gold, but at the same time, it's not that much gold. It's about 40% more gold than is currently in Fort Knox (4,582 metric tons per Wikipedia).
This is on the order of the amount of precious metals that Spain extracted from the New World in the 1500's. I haven't been able to track down a reliable source for the amount of gold, but I've seen estimates of the amount of silver as high as 41,000 metric tons. Mind you, the influx of treasure from the New World seriously disrupted Western Europe's economy, but it didn't make gold and silver worthless either.
First, realize that you're not putting all that gold into circulation as coinage in one fell swoop, even if you wanted to. With medieval technology, hauling statues weighing one and a quarter metric tons to somewhere they can be melted down will be very time consuming and challenging. Not least because with that much weight pressing on a small area, the statues probably instantly sunk into the mud of the battlefield when they were transformed. So now you have to dig them up again. Six thousand metric tons of gold hitting the market at once will cause rapid devaluation--the same amount dribbling out over years, less so.
Second, you can use gold to make lots of beautiful things. Candelabra, plates, murals, jewelry statues of religious icons (if the irony of melting down your enemies to make a statue of your god isn't too much). Hell, melt it and pour it in sheets over the outside of your castle walls as a warning to future invaders. While in some sense all this gold decoration it won't be as valuable as if gold were scarce, it will still be awesome. After all, you're not trying to sell all this decoration, just enjoy it yourself. You may lower the price of gold jewelry and decorations, but it won't immediately affect the value of the currency and make it useless for trade with other kingdoms.
Finally, even after you're done using gold for any conceivable practical purpose, you need not turn it all into coinage (or bullion) right away. Generals of the opposing army you might ransom back to their home country. Or, conversely, put them on display somewhere as a reminder of your victory. Stick a bunch more in a vault against a rainy day.
Also, obviously you can tweak the numbers if necessary to make things work for your story. Besides reducing the number of enemies who were "midased", you could always declare that they are converted into 10 carat gold, rather than pure, cutting the amount of gold you need to deal with in less than half.