Caution: spoilers ahead for The Walking Dead season 11's "No Other Way"
Alden finally dies in The Walking Dead season 11, but it's not immediately clear how Callan McAuliffe's character kicks the post-apocalyptic bucket. Maggie's food-finding revenge mission against the Reapers has demanded a heavy price. Though most of the fallen faces are expendable background characters we never had the pleasure of meeting properly, other victims held higher status in The Walking Dead's hierarchy. Season 11 wisely took the opportunity to trim away most of Maggie's stragglers (barring Elijah, who's by far the coolest), but from The Walking Dead's main cast, Alden drew the short straw.
In the lop-sided battle between Maggie's party from Alexandria and Pope's Reapers from Meridian, Alden endured the worst injuries, but The Walking Dead played coy over whether these wounds were fatal. On one hand, Alden began giving his "just in case I don't make it back..." speech; on the other, Maggie promised she'd return for him when the mission was complete. Clinging onto consciousness, Alden waited in a local church while his friends (those in better condition) went to finish off the Reapers. Alden wasn't seen for the remainder of The Walking Dead season 11, part 1.
Alden's tragic fate is confirmed when Maggie finally returns to the church in The Walking Dead season 11, part 2's "No Other Way." Hoping she'd find her friend alive enough to cart back to Alexandria, Maggie is instead greeted by an Alden-esque reanimated corpse. There's also another zombie in the building, but how did Alden actually die? Was it his preexisting injuries? Or this second zombie loitering in the church? Although Alden may not have survived long enough to reunite with Maggie anyway, small details in his final scene prove it was the Reapers who killed him.
Although not immediately obvious, Alden's corpse has its throat slit. Callan McAuliffe's zombie form has also been reduced to dragging itself across the floor, whereas Alden could at least hobble around gingerly when Maggie last saw him. These extra injuries (the slashed throat in particular) prove Alden was found by a Reaper after Maggie left him, the poor guy forced to fight despite the copious amount of claret already pouring from various holes that shouldn't be there. The second zombie Maggie finds wandering the pews is dressed in Reaper garb, which implies Alden managed to at least take his murderer down, and give the Meridian team one less enemy to worry about. Maggie handed Alden a knife shortly before they parted ways - likely the weapon he used during those dying moments.
Dying at the hands of a Reaper makes considerably more sense as a way for Alden to exit The Walking Dead. What would be the point in season 11, part 1's "left in the church" sub-plot if Alden was destined to die by wounds he already had? Knowing a Reaper did it services both Alden's storyline and Maggie's. When Maggie learns her revenge mission cost yet another dear friend, it's the bloody icing on a guilt-laden cake - a final figurative stab through the conscience. The off-screen image of Alden heroically fighting a Reaper, however, speaks to his virtuous nature. Alden was always striving to help his allies, and taking down a villain in his final moments is probably how he would've chosen to bow out.
Alden's sticky fate was foreshadowed way back in The Walking Dead season 11's "Rendition," when Pope finally revealed himself. The Reaper leader purported to share a special bond with God, who apparently spared him certain death from a burning building. Pope also described a "church on the edge of town," which is likely the same building Maggie left Alden in. If Pope's Reapers were already familiar with their local place of worship, Alden's hiding place was always going to be rumbled. Sadly for him, that's exactly what happened.
The Walking Dead season 11 continues Sundays on AMC.