Focus on Buttigieg's lack of black support seem kind of weird to me. Like he's not destined to do poorly with black voters, especially if he does well in Iowa. And I'm aware that the whole "black people are homophobic and won't support him" discourse is not present on this site, but that's a bad take too that people seem to have.
In a scenario where Biden implodes and Buttigieg wins Iowa, I don't think Biden's support would move as a block to Warren/Sanders.
Pete's going to have to put the work in but he might be seen as more electable than Warren/Sanders by that point. He's running as more of a moderate and sans Biden, he'd probably get establishment support. He's comfortable talking about his faith which is a plus campaigning in the South. I could see him getting enough support to get the nomination.
It would be quite a bit different than 2008/2016 with African-American support being split between the candidates more evenly.