Yeah, stamina might be a concern for Loki. He's got a lot of power. But, chances are, using all that power will take a lot out of him. He might have a similar "time limit" like Luffy has in Gear 5. Even before Awakening. As we've seen with Luffy...Awakening a Fruit can actually drain your stamina even more than the "base" form of your Fruit. "Awakening" might actually push Loki's tolerances over the edge, and could be what does him in. "Awakening" might be Loki's downfall.
Although, this entire situation would be a good chance for us to see Loki finally Awaken his Fruit in real time.
And...it'll be interesting to see what the Awakened version of Nidhogg is. Because, there's every possibility that this is actually another "Secret God Fruit" like Luffy's Nika Fruit. We already know the War God had similar abilities to what Loki has now. So, Loki's abilities after Awakening could be completely different than his current Dragon form. The Gods seem to have...strange powers, in this World. If Loki is another "Secret God", he'd likely have a completely different form to match his new powers.
Personally, I'm wondering if the War God and the Earth God are actually the same entity? Like how it seems likely that the Sea and Rain Gods are likely the same entities, just with different names. "Elbaf"'s rivalry with Nika sounds a lot like the situation between the Sun and Earth Gods in the First World, to me. But, we'll see. The War God could be it's own, separate entity.
So, personally, yeah, I'm betting Loki isn't Awakened, yet. If only because he hasn't been really pushed to his limits, before. And if Loki does Awaken his Fruit, I wonder if Loki would be surprised how draining it is, even on his sturdy body. Other attacks may or may not be a problem, but overestimating his own strength could get in into some trouble.
