In my opinion, no song should ever be retired -- not an I&W song, not a WDADU song, not a Majesty track should be put on a "Never to be played, ever!" list. James LaBrie very clearly couldn't keep up with a full album performance of I&W as-is, so they tuned it down a semitone. Rush did that, even going further than that for some songs, and it allowed them to continue playing classic fan favourite songs up to and on the R40 tour that Geddy Lee simply couldn't keep up with anymore.
So, in terms of LaBrie potentially having trouble with some songs -- not an issue, IMO. DT have shown they're willing to tune songs down, it went down a treat, no reason they can't continue to do that for any problematic songs or runs of songs, and as always, any particular sections of songs, LaBrie can easily just sing an altered melody(See: Take The Time circa 2002, Learning To Live circa 1999-2002, Don't Look Past Me circa 2017). So, in terms of taking songs out of rotation for vocal reasons, I would say absolutely not.
With that out of the way, the only thing that really leaves is the idea of songs that shouldn't be played for reasons such as the songs themselves being "Bad"(Bad is in quotes as I would say it's a poor word to use, given how subjective all this is), or personal significance, like with Best Of Times. I think the thing about all this is that if the band feels the time is right to play any given song, they should play it. Whether that means bringing out New Millennium(A song JLB isn't a fan of, and thus is unlikely to be played live again) for one last time before retiring it, or doing whatever is necessary for it to be okay for them to play The Best Of Times, even if it's only done as a one-off under special conditions.
So, I don't think any song should ever be off the table. No, not even Raw Dog.
Though, having said that, I'd be really glad if they do stick with the idea of never doing any medleys of any kind ever again; if you're going to play 10-15 minutes of instrumental greatness, just play Stream Of Consciousness in full. Instrumedley was a pretty neat thing, but I'd prefer just hearing a handful of the individual songs contained within it than hearing just little bits and pieces.