Could There Be A Reason For Jon's Resurrection?
Of course, there are a few good things to come from Olly's betrayal and Melisandre's magic. For one, it supports the fan theory that Jon Snow is Azor Ahai, and will therefore be the one to save Westeros from the Night King and his army. Jon's death also plays into a few other theories; that Daenerys' curse (courtesy of Mirri Maz Duur) has been broken, for example. Finally, this allowed Jon to leave the Night's Watch without breaking his oath, having served to his death. Result: an honorable King in the North who knows the Night's Watch and the threat of the Army of the Dead.
However, all of this could potentially have been achieved without actually having killed Jon at all. The prophecies surrounding both Azor Ahai and Mirri Maz Duur's curse are so vague (in the general style of prophecy) that it would definitely be possible for these to be fulfilled or dismissed without a literal death. As for his departure from the Night's Watch, well, while Jon has shown that he is noble and sticks to his oaths, he has also shown that he's willing to use loopholes within those oaths to get what he wants (most notably Ygritte, who wasn't technically his wife, as he points out to Sam). As Lord Commander, Jon could have bent all kinds of rules in order to allow him to become King In The North at the same time - if the business of the Night's Watch is protecting against White Walkers, and becoming King is the best way to do that...
Jon Snow Can Still Die Again
At the end of the day, though (or at the end of the show), Game of Thrones can still get past the terrible decision to kill Jon Snow - and it all comes down to the final season. There is a whole lot to wrap up here, and Jon Snow is going to be in the thick of it from the start. While his season five death meant that season six and seven death-fakeouts lacked impact, now that the show is almost over, major character deaths are going to come back into play. The fear fans will feel for Jon will be just as real as it was before he was killed in the first place. Whether Jon ends up dead, King in the North, back at the Night's Watch, or on the Iron Throne itself, Game of Thrones may finally be able to put this terrible non-death behind them for one last fight.