I see this as a 50 win team with Hayward continuing to struggle.
If Hayward improves, it can be a 55-59 win team depending on how well he plays. Above average starter more in mid 50s win range. All Star into high 50s.
If Horford goes though .... everything crumbles. He is the guy that makes everything come together. Who takes individuals and makes them a team. Without Horford, this is a team that struggles to make the playoffs. That needs Hayward to play well to make the playoffs. If it gets a bad Hayward, they probably miss out on the postseason.
Keep Horford. Desperately keep Horford.
This will get hard to watch quickly without Horford here to make this team's defense and this team's offense work effectively. The offense even more than the defense. Lots of iso ball without Horford around to create ball movement.