First, let me say that this is clearly supposed to be an abstract question, so we should assume that WCW wasn't going downhill and that they would've managed to keep a TV deal with or without Time Warner.
That being said, even though I was always a diehard WCW mark and only started casually re-watching WWF(e) for maybe a half a year before WCW got bought out, I still think it would've worked out poorly, at least in the first couple of years; but I suppose I can say the exact same thing about the Invasion angle. I think the most important thing to take into account is the extensive list of people who were misused in WCW who had success in WWE (either before or after their time in WCW), most predominantly Austin, Macho Man, Bret Hart, Jericho, Benoit, and Guerrero. I also think about WWE talent that WCW would've misused if given the opportunity: The Hardyz, Edge, Christian, and The Rock all probably would've suffered career-wise. The only real plusses I can think of is that Booker T and Ernest Miller would've enjoyed better careers and more deserved time in the limelight.
As for announcers, while I don't think Tenay honestly gives a crap about wrestling anymore considering his current time in TNA, he was my favorite announcer back in the days for his well-rounded knowledge of professional wrestling and to me that was always more important than people like Jim Ross who were more or less glorified hype-men who could name about five wrestling holds and generally still call them wrong. A table of Tenay, Lawler, and anybody but Schiavone or Ross announcing for Nitro would've been a nice mix for me, especially if WCW managed in this hypothetical situation to pick up Joey Styles from ECW.
I think WCW's best shot would've been to go back to doing a three-hour Nitro to be able to display all of the talent they would've resultantly been glutted with, and with the first hour dedicated to a would-be vast cruiserweight division (now with the Hardyz, Christian, X-Pac, Jerry Lynn, and Tajiri in the mix), maybe seeing Hardyz doing something with fellow OMEGA stars Helms and Moore. I think that could've been at least better than WWE's sloppy unsuccessful Invasion angle.
Still, as much as I try and think about a way to make it work, I can't get around WCW's cockamamie booking and abhorrent waste of talent. The only real bright spot I can think of is that HHH would no longer hold any power and I wouldn't have to worry about watching him main event for the next seven years or helping his mediocre buddies out. And, even considering the wasted talent, the overall product might've been better down the road at least in comparison to the current WWE product, which I have no love for. If there were a world where just being Guy in Black Trunks #5 didn't automatically qualify you for the main event, I'd be satisfied.