As much as I hate to say it, it seems guaranteed to happen. It just seems inevitable. Once Durant's contract is up, he will join LeBron and dominate the league. Durant in his prime, will join LeBron at the end of his. They will dominate the league, and as LeBron approaches the end of his prime, Durant will join him in the middle/start of his. This will lead to them winning 4+ straight titles
Why does it seem guaranteed to you? I cant see they happening. KD has a superstar teammate in Russell Westbrook and a young core that can be molded. Carmelo is the more sure bet.