The Miami Heat goes and gets another first-round pick
Let's say the Cleveland Cavaliers get to a point and tell the Miami Heat that they don't want Tyler Herro and would much rather have an additional first-round pick instead. There could be a path where the Heat recruits a third team to help make it happen. Dating back to the offseason, there was a belief that the Nets were interested in Herro. I'm not sure if that's still the case, but we'll use Brooklyn as a placeholder that represents a third team. It could be the Nets or any other team with an expendable future first-round pick that also has an interest in Herro.
In such a deal, the Heat could send Herro to that third team (in this case, the Nets) and send an additional pick to the Cavs. Overall a package heading over to Cleveland could end up being something like Duncan Robinson, Caleb Martin, Nikola Jovic, and three future first-round picks. If Cleveland wanted, Miami could also throw in pick swaps or even a couple of second-round picks.
This has to be viewed as a pretty strong offer and one that would have a good chance of being accepted by the Cavs. If the Heat genuinely believes Mitchell is a missing piece for a championship, this is a path Miami must be willing to explore.