They will still be contenders. Lebron will still be Lebron. They will likely retool with a new crop of ring-chasing free agents and redesign their offensive system through the Lebron/Bosh/random 3-point shooter trio rather than the current Lebron/Wade/Allen system.
The East will still be weak. I see the Pacers taking a step back this season; I have never been high on that core, I think they have been overrated and overachieving as it is. I think Lance leaves and they don't find a suitable replacement. Paul George will be great, but the rest of the team will be mediocre; I predict them limping into a 3 or 4 seed and not making the ECF again.
Besides that, the only teams out there that can make any noise are Toronto and Brooklyn, but I don't see either as being a particularly ferocious post-season team. In fact, I think Brooklyn will be worse this season than they were last season. I just don't trust that core (and this as someone who loves Paul and Kevin with all my heart) to put it together on a consistent basis. Toronto is talented but young and uneven. Then there will probably be one more solid team out of the East, depending on what happens in the draft/free-agency; either Chicago, Boston, Atlanta, or a wild-card like Philly will make some big moves and have a good season.
I see the Heat at least in the ECF next season. I don't see them winning a ring (barring a real free-agency steal. Kevin Love for the vet's minimum?), or necessarily even advancing to the Finals, unless all the other East teams take a step back.