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Yuzuru gets reincarnated/reborn in the same universe that contains the main world timeline, but on an alternate and better timeline.Yuzuru finally moves on from the afterlife.Events in the Angel Beats! anime sequel (if ever released) could take place here.As per Angel Beats!: Another Epilogue, Yuzuru remains in the afterlife for an undisclosed amount of time helping others move on.Kanade moves on from the afterlife after thanking Yuzuru for the heart he gave her.Events in the Angel Beats! anime take place.She stabs him in the chest and notices that Yuzuru doesn't have a heart.
Kanade and Yuzuru finally meet in person. Events in the Angel Beats! Heaven's Door manga take place. As per Yuri, Kanade was there before she arrived, but, we're never told for how long, so, the amount of time she spent there from her arrival to her departure is unknown. We don't know how long she lived after her heart transplant, but, it apparently saved her life, so I presume she lived a good while after it. Kanade is in need of a heart transplant. Because the rescuers arrived just barely too late, his organs could be harvested in time. Just before he dies, he signs an organ donor card. Although he survives the initial crash, he eventually dies of thirst. The ranges of the circles/ovals are rough estimates. The blue lines represent Yuzuru's transition from one timeline to another. The white lines represent Kanade's transition from one timeline to another. The blue circles/ovals represent the time Yuzuru Otonashi spent on a timeline. The white circles/ovals represent the time Kanade Tachibana spent on a timeline. The cyan line is the alternate world timeline where (I presume) the characters in the series went after they've resolved their issues and regrets in the afterlife and moved on. The red line is the afterlife timeline where the characters went when they died and where most of the series takes place. The green line is the (main) world timeline where the characters in the series lived their lives before they died. I drew up this little image of the three different timelines that are present in the series: However, if we assume that the series follows the basic concept of eternity, then a partial explanation can be given.
Unfortunately, Angel Beats! doesn't go into much detail about the mechanics of the afterlife environment it takes place in.