Boy I don't even think in terms of them having a heir.
In my musical world most of what I'm listening to is obscure. Bands like Analog Missionary and Chon. Both progressive. I suppose a mix of that kind of music, exotic jazz, classic prog/hard rock, and Classical fills the vacuum.
The Holst Planets by André Previn & Royal Philharmonic Orchestra has been a constant presence. The Who Tommy. And strangely Sammy Hagar who I've generated a grudging respect for both as a song writer and performer.
One of the things I appreciate so much about Rush is being able to stop listening to them for a little while, and return to their music- I always hear things I had not noticed before. The arrangements and harmonics are so dense.
So I'm not looking for a replacement.. Perhaps more for something compelling and new. Given my tastes that would most likely be something musically progressive.
Regarding YYNOT- that's just fun for folks like us. Though I'd be very happy if they could "make it" based on their musical style since the writing is so good. I'm not sure a sonic clone of Rush would remain relevant. Especially considering I fully expect more Rush music- even without a tour.
YYNOT has killer chops though. Back when I played music for a living I would have given a limb to have that bassist play on my studio stuff. Well.. ok not really. But close. Bass players like that are so difficult to find.
Actually- the talent in that band, as a whole, is difficult to find. But that bassist is a rarity.