A few different ways to look at this.
The Raiders, clearly, have not taken advantage of the full haul that was sent their way---And it was indeed *quite* the haul. In a vacuum, the Bears are better off with Mack than they would've been without him. The unknown is what the Bears would've done with those picks.
The other side of it is that the Mack trade took the gamble that Trubisky was your guy. If Trubisky didn't play up to par, Mack's performance would've ultimately been wasted. That's essentially where we are now. 2018 was a hell of a lot of fun, but the Mack trade---taking Trubisky, the coaches' and offense's performances into account---ultimately really wasn't worth it.
Unless Fields comes in this year, balls out, and leads the Bears to a Super Bowl ASAP, the Mack trade was wasted, and with it a bunch of picks (that the Bears may have fucked up anyway, but still...)
The earliest you could really cut or trade (haha!) Mack would be next year, when his cap hit will be $30 mil and his dead cap "only" be $24 mil. Year after that, it's $28.5M and $11.6M. We've clearly seen Mack slowed down by mileage and injury, and I don't suspect it will get any better, aside from fairly solid play and some flashes of brilliance here and there.
TLDR: It depends how you look at it. Mack delivered his first year, and has been fairly solid since, albeit with some injury and sluggishness included. But taking into account the lack of offensive growth or any deep playoff runs multiple years later, while giving away some potentially valuable picks, it would be hard to say the trade was worth it in the end. Such is life.
