TP for the OP, this is a pretty creative trade. I clicked this thread expecting Love for Crawford, Wallace and Brooks.
If MIN would do this I would too. Dieng is a really good prospect and the salary is about even in the long term. We get out of an extra year of Lee which helps us. Williams still has some chance of being good, at least bench-worthy. I suspect MIN would only do this if they really wanted out of Williams contract.
Here is my only concern. From the little I know about our locker room, Bass and Lee are both pretty good friends with Rondo. I'm not saying we can't trade them or even that we shouldn't, but we have a mercurial PG who has been kindly described by them media as "moody". It might be worth talking to Rondo about this trade because it doesn't make us a lot better, even down the line.
For the record I really like Dieng, I wanted him in the draft, just not at 13 :/ I think his ceiling is Sam Dalembert and that is certainly worth acquiring at this point.