Is it just me or he stabbed himself in the same place as Ai? Then that's gotta be fatal then
Well, I just went balls deep researching about stab wound when Aka left Ruby stabbed in the cliffhanger and here's the result of that labor:
First, Ai was stabbed pretty much in the middle of the abdomen. Judging from the the time she has before she lost consciousness, it likely missed the major blood vessel, but hit her major organ, so she bled and died very fast.
Now, for Aqua on the other hand, he stabbed himself about lower left of abdomen, and the knife he used is pretty short, compare to what Nino or Ryosuke used. I'm no expert in anatomy, but there shouldn't be major organ there excepts bowels, so there shouldn't be major blood loss, only a very high risk of infection from all the waste & bacteria in the intestine, but that is a complication down the line that would mess with his survivability after treatment, not to the immediate situation. I would hence assume this stab wound wouldn't really kill him that fast and he has a high chance to survive long enough to be taken to hospital and treated. The more concerning issue would be the fall, but then again, we can see the possibility that Aqua will fall on top of Kamiki who will cushion the fall and survive.
So... main question will be how quickly can he be brought to hospital? The area looks remote though.