I think Mase would have lasted for a good time period in hip hop and he'd probably be running his own label by now after he fulfilled his contract with Diddy.
I theorize that Mase would have been the one to bring out some of the big name 00s era producers out in his collaborations. I distinctly remember an interview in which Mase (promoting his Harlem World group) bragged about and name dropped little known producers for his group album: Neptunes, Just Blaze, and Kanye West. Sure, the album was mostly garbage but I think those producers would have keep working with the man who gave them their biggest shot so far. I think Mase would have learned what went wrong with the album by following the Puff Daddy sound to the extreme and would have went the other way. Harlem World would have disbanded. But the producers would have come to him with some of those beats they had worked on their own and went to other artists with.
Collaborating with Nelly and DMX would have kept momentum for him when the sound was changing in hip hop.
As far as other artist:
Cam'ron and the Diplomats would have blew up the same as they had with or without him around as far as the cult like movement. Things might have changed slightly since they might have been using the same producers at times.
Loon would have NEVER had the solo shot had Mase not left and Fabolous would have been in the Ghetto Fabolous/DJ Clue level-mode of his career for a while longer.
Here's why:
Loon was brought on to the "I Need a Girl" songs as more or less a sidekick substitute. If he thinks it's anything but a coincidence then he's lying to himself as to why Diddy chose him.
DJ Clue knew how he was anchoring Fabolous to the general public. He produces the song "That's the Way" for his "Professional" album to associate Fab with Mase: the song was clearly meant to be put out as a single. Then he gets Diddy who's on the "I Need a Girl" phase of his career to do the remix with Fabolous in the sidekick placeholder.
"Trade it all part II" was where Fab's career really took off. Ghetto Fabolous finally goes Platinum after a year of being on shelves and that song influences his next round of hits as he becomes a platinum selling artist: "Can't Let You Go" "So Into You".
"This is my Party" similar in style to "Young'n" does nothing, BTW.
Fab has the better punch lines, sure. Fab is in his own lane now but if it had not been for the sidekick placeholder position: he would have took a little longer in finding an audience.
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I'm eager to see how an album of his might actually be if he actually put in more of an effort this time around. Double Up was just patched together and Welcome Back was a half-hearted effort but impressive in that he recorded it all in a few days after a 5 year break.
He's still got it IMO.