I don't buy the report that he has negative value at all. he doesn't have great value, but that is mostly because he is a secondary or tertiary star due big money and is on the wrong side of 30. He is, however, a very good player.
Before we traded Hernangomez I was proposing something like this for awhile
McCollum for Richardson, Hernangomez, Nesmith, Langford, 22 1st, 24 1st (top 4)
I still think that is probably the right sort of value, but if this report is to be believed, then maybe you drop the 24 1st. Since Hernangomez is gone, the salary needs to be reworked some.
McCollum for Richardson, Schroder, Nesmith, Langford, 22 1st
I think that makes pretty good sense for both teams as I'd rather keep Horford and I don't think they'd want him anyway so it might cost some extra stuff
If they'd give up Covington, it could be altered with Horford
McCollum, Covington for Horford, Nesmith, Langford, G. Williams, 22 1st, 24 1st (top 4)
I'd probably prefer the 2nd trade, but either one would be fine
So if the 2nd trade is made (2 open roster spots)
PG - Smart, Schroder, Pritchard
SG - McCollum, Richardson, Dozier
SF - Brown
PF - Tatum, Covington, Fernando
C - Williams, Freedom, Bol
Team would need to pick up a center with 1 of the open spots for sure, but the other could be pretty much any position. Definitely a tax team with that roster, but that team is a lot deeper and adds an influx of talent and thus would have a much better shot of actually competing in the post-season, both this year and in the future.