Yes, now I'm pretty sure that the Moriarty we know is posing as a simbol and is going out there instead of the real one. Hey come on a criminal mastermind that "rules" the world in his own way would never put him self in a danger like that, way to greedy and values life very much, which would explain why the poser Moriarty killed himself, It was a contrast, a contrast that Sherlock will figure out or he already did, It's a message "I will never die".
I guess we get to meet some more posers in season 4, I doubt we will be seeing Moriarty soon. 
I owe you? Well he is probably thankful for the fun Sherlock provided him, but I'm afraid that "Moriarty" is on a whole different level than Sherlock, just becuase of his power.
Explains why The Poser got a phonecall at the pool. Things obviously were getting out of hand, Sherlock had his gun up to the bomb, Moriarty still has plans, orders a phone call to "distract" the poser Moriarty so he doesn't show that he missed that one move that Sherlock made there. The real one is changable, he did want to eliminate Sherlock, let's keep in mind that he is a psychopath, and he would never get to the position he is as a criminal consultant if he let the ones who get close to him live. That's not how criminals work. They don't play around much. I think the whole "Game" Was to try and scare Sherlock, that didn't work, and + he missed a few details, So, he doesn't want to show his weakness to Sherlock, to Sherlock he wants to stay "The perfect criminal", no mistakes, no flaws. So... What does he do? Eliminate the only connection that Sherlock had to him, kill off the Poser. The Moriarty we know, is not alive.