I dont see Lebron going back to Miami, even Wade. But Lebron says that he wants to play with Paul, Wade and Melo in the future. If this will happen and any team that have capspace for them will likely sign them all.
They are too old to win a championship IMO. and for me that is not good if they will joined together as it is too late already. They will be beaten by the young and more athletic stars like Anthony Davis and even Lebron's team can easily beat them for sure.
Are you really a NBA enthusiast? Have you seen those old players still taking championship despite of age? One good example is the players from San Antonio Spurs. We all know that Duncan-Parker-Ginobilli able to take championship in 3 decades year (90', 20's, 21's) and for the record it was 5 titles.
And honestly, if possible, James, Paul, Wade and Melo's combination in the future will really has the capability to outshine all of them even all 4 will aged at 35 years old above or close to 40's.