again, I think people get hung up on fire arms and automatically think "machine guns". There is no need for all that. A flintlock would fit in just fine. Heck, when you think about it, destruction staves are kinda like guns already. All it would take would be a skill tree around using staves and you would have gun paly by de facto.
On the other hand, I would love a smooth bore single shot rifle that does more kick than crossbows but takes much longer to reload. Guns in high fantasy have been around for a long time. Look up War Machine/Iron Kingdoms as an example.