Almost immediately after reviving Captain America in the Silver Age, Stan Lee and Jack Kirby began foreshadowing Rick Jones becoming the new Bucky. Rick finally took up the mantle and became Cap's new sidekick in Captain America #110... only to be written out of the book in issue #116, with Rick eventually becoming bonded to Captain Marvel over in the Retool of that character's series. Lee and artist Gene Colan would instead introduce a new partner for Cap in the form of The Falcon not long after.
Steve Rogers dies in Dan Jurgens' Captain America vol. 3 #50 stopping a nuclear warhead, it seems like he is really gone, and there is a big funeral with all his friends. Then Marvel acts like the whole thing ever happened and picks up with no mention of any death.
Mark Gruenwald's final Captain America arc had Steve slowly dying, which led to him training a pair of young heroes named Jack Flag and Free Spirit to take over for him. Mark Waid then took over the book and promptly cured Steve, allowing him to get back into the action. The subplot about Cap's new proteges was dropped entirely, and Jack Flag wouldn't be seen again for roughly a decade, while Free Spirit wouldn't appear again until twenty years later.
Captain America and The Falcon ended with Cap finding Falcon's costume fluttering in the wind, with it left ambiguous as to whether or not Falcon was dead. This was going to be resolved in a solo Falcon book by Christopher Priest, but the series never materialized, as Priest didn't want to be typecast as only writing black heroes.
In the 70s, a crossover between Captain America and the X-Men implied that The Falcon might be a mutant. This was dropped until a decade later, when the solo Falcon series confirmed this theory by having a Sentinel identify the hero as a mutant. This was ignored until 2001, when Kurt Busiek addressed the inconsistency in an issue of The Avengers, where it was established that Falcon was not a mutant, and that the Sentinel had simply been malfunctioning.
When Steve Rogers returned after his supposed death in Ed Brubaker's run, Bucky — who had been acting as Captain America to honour Steve — insisted on giving the Captain America mantle back, even though Steve didn't want it. Steve insists that Bucky keep the title, and justifies it by saying that Bucky has moved beyond using the role to honour him. He later confides in a sleeping Sharon Carter that he'd had a vision of a possible future, and in this future Bucky, as the Winter Soldier and not Captain America, dies after being impaled on debris. Also seen are numerous large tentacled silhouettes and someone wielding Thor's hammer, Mjolnir. The Fear Itself crossover, where numerous Mjolnir-like weapons fall from the sky and Bucky was seemingly "killed" (but as Captain America), could be the follow-up, but it doesn't quite line up. The tentacle things never appeared and besides the event being Thor-related, there aren't many similarities. The visual of giant tentacled robots would be used years later in Secret Empire (and a CBR article theorised that this could be a case of Arc Welding), but that's it.
Brubaker's Steve Rogers: Super-Soldier miniseries ended with Prof. Erskine's grandson intending to create new super-soldiers by recruiting test subjects with similar backgrounds to Steve Rogers, eyeing a sickly teenager in a poor neighborhood who recently lost his mother. Never seen or mentioned again.
Near the end of Rick Remender's first run, Sharon Carter returned after she was previously thought to have died in Arnim Zola's Dimension Z. She immediately accused Zola's daughter Jet (who had betrayed her father and sided with the heroes) of being a Mole, and demanded that the girl be gagged so that she couldn't even defend herself against the accusations. Offended by the claim, as well as the heroes' willingness to believe it, Jet abandoned them and returned to her father's side. The way the situation played out made it seem like Zola might have been behind Sharon's mysterious return and actions, and that her accusations may have been an attempt to frame Jet to get her to turn against the heroes. However, this has never been addressed since then, and Jet ended up in Comic-Book Limbo after Remender left the book.
In All-New Captain America, Misty Knight dropped the bombshell revelation that government organizations like S.H.I.E.L.D. and various superhero teams like the Avengers, X-Men and Inhumans had been infiltrated by Baron Zemo's new HYDRA. Again, Remender left the title before this could be further explored. While the later Nick Spencer run opened with Sam and Misty taking care of the last HYDRA moles within S.H.I.E.L.D., the thread about HYDRA having plants in the superhero community was largely ignored.
