You going to sue Nasser now for telling the truth?
By definition, slander, libel or defamation in general is only so because it's untrue.
Assume you say I'm a terrorist, known only as Cobra Commander, who leads an organization, Cobra, and we plot to conquer the world. I could sue you because I can prove that's ...
Err, drat -- bad example.
COBRAAAAAAAAAAAAAAAAAAA! 
Nah, you can't sue a dead man. And in civil court, Milos would actually have to prove that he didn't do the things of which Nasser accused him. That's pretty tough. Moreover, per the oldest tenets of libel law, which I abbreviate PODAF, Milos would also have to show that ...
*Nasser's supposed lies were "published" which, in simple terms, means were communicated to a party other than Nasser and Mishko.
*Of and concerning Milos -- no problem there.
*Defamatory. Illegal drug use qualifies.
*At fault. This simply means that Nasser or the means with which he communicated the defamation did so with the knowledge that said information WAS false. Or that might fall under the negligence clause. It's been awhile
*Falsity. This is the biggie.
It's entirely possible someone like Milos would face extra conditions as a "public figure," however, in which case he'd have an even higher burden of proof. Basically, the lawsuit would win or lose upon the truthfulness of Nasser's accusations AND how those accusations, if false, adversely impacted Milos' standing in the community; e.g., if the charges hurt his ability to find employment, join certain community organizations or the like, if Nasser lost the case, he'd probably have to pay a modest amount of money in what's called damages (Milos' court costs, sometimes even the money he could've earned at X or Y jobs if Nasser hadn't circulated the lies -- that sort of thing).
It's obviously a moot point now, with Nasser dead and buried. I somehow don't particularly doubt some of the things he said about Milos, but I have a strong hunch he was extremely bitter toward Milos -- remember that "Delusional Clown Milos" bullshit, even years after Nasser and he'd apparently crossed swords? -- and Milos is NOT the only person who said that Nasser took great pleasure in schadenfreude. To add to that, Milos isn't the only guy who said Nasser had a propensity for exaggeration and even outright story-telling.
I do not doubt that for a second. I remember Nasser and his "mighty" 15 reps with 225 in that stupid Weider/Muscletech challenge. I will give Nasser this: his reps were all perfect, and it was clear he had a good bit more in the tank. But when he took the microphone, he blabbed some pure Angus-grade bullshit when he wheezed that he wasn't "used to doing such high reps after doing 600 lbs. for a few on bench press." I remember those Team Nasshole idiots defended him and said he literally "threw" the contest because he wasn't interested, but then, those were the same guys who couldn't understand why Nasser was apparently "shunned" at an ASC event some years back that featured all of the previous champs. (Nasser was a no-show. Maybe he had to detail a car. Who fucking cares anymore.)
Nah, Nasser was a bullshitter. I wouldn't call him a liar outright, but I know some of the things he said about Kovacs were fabrications (Greg having to get his wife to wipe his ass with towels, for instance. Don't ask me how because I cannot say -- and no, I don't know Greg. Personally I think the dude is a trainwreck and his whole "I'm so strong" spiel was an utter embarrassment. But from what I HEAR, Greg is actually an OK guy, just kind of a big, dumb farmboy. And yes, also from what I hear, Nasser sold the guy short, even after completely abusing Greg and his family's hospitality for a month or so.). He had a fantastic physique in his prime, but IMHO, as much flak as Yates catches for his '97 shape, Nasser was actually LUCKY to finish second to him. I had Levrone in a solid second for that show ... and interestingly enough, K-Lo went on to whip Nasser's ass at all but one of the Euro Tour shows that year. Then Kevin introduced coffee and vodka to Ronnie, which let the Ronster smoke them all at the Russian Grand Prix
