This is a complicated trade that completely assumes the Portland Trailblazers flip the switch, to collect young players and draft picks and work towards a rebuild without completely trashing the team.
This trade would likely work better with a team that had a little more flexibility than the Heat, but you could see the Heat attempt to swing for the fences and try to grab another star while they still have a shot in the weak Eastern Conference to make some waves. It's hard to imagine if either Dame or McCollum come on the market that the Heat wouldn't be buyers.
Celtics obviously need to upgrade, but it's hard to track exactly where. Walker is a solid PG, but Lillard offers far more scoring and distribution for not much more $$.