Assuming you're always wearing your shield, and there's no reason why you shouldn't be, then the chance of dying is very small. Even if your potion does run out, the damage it hits you for is very low so it's nothing to worry about. As I said above training magic usually costs you money, and although this type of magic training is slightly slower than most methods the fact that it'll probably make you several million if not 20 million runescape accounts with the draconic visage drop as opposed to when I trained my magic losing around 20 million gold you can see why to many players this is something definitely worth doing.
Killing them using magic is really useful because unlike melee you don't have to get up close to them, once you start getting up close to them they can use their own melee attacks and deal you damage. If you use magic spells from a long distance you can protect yourself from receiving rs gold any damage from their fire breath attack. If you have both an anti-dragon shield as well as an antifire potion you can stop yourself taking any damage. Their fire breath has the potential to hit 300-400 damage on you, wearing the shield reduces this down to about 30-40 damage, and then drinking the antifire potion takes this down even further to 0 damage.
I'd say there's one really great way of making money on runescape gold using P2P magic, which is quite rare because magic is one of those skills which you tend to lose money on and not gain money using, similar to construction or herblore. Killing metal dragons is a great way of making money because the monsters drop quite good consistent drops netting you several 100k an hour in profit. But when you look past that you also get the chance of receiving a draconic visage drop and those are worth around 18 million gold pieces which means they're going to be sought after by practically everyone.