Well, there are two issues here.
First, there is the question of whether Lebron leaving the Cavs makes him more of a threat in the next couple years. To that, I say, absolutely. Obviously, it depends on the details, but if you pair him with someone like Bosh, and then a couple other quality players, then it would absolutely be more dangerous than having him on the Cavs, who are all but stuck with the roster they have, which is decent, but still lacking that true #2.
The second issue is with the C's. I have been saying for a while that I do not think the C's will be basing any major decisions about their core on this playoffs, and I stand by that. I have however, changed my mind a bit about the C's chances to contend for another year or two. With the way Rondo seems to be making the leap, and just as important, the way his teammates are finally accepting him as the star of the team, I think they absolutely could contend for another couple years with this core. They would need to get lucky with health, and reinforce it a bit, but I think its absolutely possible.
I still think Danny will be open to making any trades this offseason that bring back good value to help them reload, but now, I don't think it will be such a negative, if they can't find the right deal, and need to stay the course, waiting for some contracts to expire, if nothing else presents itself.