First of all, it seems like most of the new Avengers die, not just Spidey and Black Panther (and it's at the very end)
Also Disney knows people want to see Spider-Man in the Avengers movies so I'm sure it won't be long until the finger snap is reversed in A4. And now that they see Black Panther breaking all kinds of records(hell, it might make more than Infinity War), I'm sure he'll play a much more prominent role in A4.
So stop bytching. Most of us wanted Thanos to win anyway, at least in this film. I'm sure his defeat in the next film will be epic. Besides...
Avengers (2012)
Avengers Age of Ultron (2015)
Avengers Infinity War (2018)
Avengers 4 (2019)
It's just one goddamn year. Obvious two-parter, fukk what the filmmakers say.