I said no. While I'm a huge Portnoy fan, I still want to hear more from Mangini. He's an absolute monster behind the kit and they haven't even began to tap into his potential. I wouldn't want him to turn into another Derek, where he's gone before he even gets the chance to put in his best work for them (although Derek being fired did lead to Jordan joining so it worked out for them).
The Jordan for Kevin part was a much easier no. Jordan Rudess was the single greatest thing to happen to Dream Theater. After struggling to find their way musically after Kevin left in 1994, they finally found the missing piece of the puzzle that would tie it all together to get Dream Theater firing on all cylinders. What Jordan brings to the band in terms of musicianship, creativity, and passion can never be overstated. My favorite story that shows how great Jordan is for the band involves what is one of the most popular sections of music in Dream Theater history: the ragtime solo in TDoE. In Jordan's instructional DVD Keyboard Madness, he was giving a little backstory behind the part before he showed the layers in that particular patch. He said that it originally started as this serious riff on the guitar and he just threw out the idea of changing it to a ragtime piano part. The rest of the band went with it and it ended up working perfectly. The ragtime sound fits so well with the craziness of the song, and we have Jordan to thank for coming up with the idea. I can't say enough good things about him. He is the greatest keyboard player of all time and getting rid of him would be making DT worse.