Yep, it happened. Although Mars and Jupiter were no problem at all thanks to Fandango's Steel-type and Substitute, Cyrus was a completely different story. I went into that fight steeled for the worst, and not only was it as bad as I was prepared for, but that Gyarados literally decided to be Chuck's Poliwrath all over again. Three of those four deaths were to that thing alone, two of them (Quadrille and Minuet) without a scratch on it, and it scored two critical hit Waterfalls in a row, one was unnecessary on Minuet because he was below half health anyway, and the second was an OHKO on Bunny Hop after ThunderPunch did less than 3/4 his health - which was good, because he didn't heal, allowing Freestyle to kill it, Weavile and Houndoom afterward, and do over half to Honchkrow. Had he healed Gyarados after it killed Bunny Hop, that thing would have swept my team.
I haven't chosen my replacements yet, but aside from what you mentioned one other thing I have that might prove interesting is Moonwalk the Clefairy, which I caught at Mt. Coronet's mountaintop just before the big events, and can learn Cosmic Power and Moonlight along with a slew of other attacks. Route 222, which will probably be my final encounter of the game given I have basically everything I can obtain after that, does provide me with a chance to get Electabuzz, but by then i'll have already formed my new pairs.
In the thread for that challenge, there was something I discussed wanting to do on Black 2 to follow my Personalocke with. Something that will likely seem intimidating... I'm probably going to start playing that before I even get to Victory Road in Platinum.