I'm sure the ride will be fine. Uni hasn't disappointed yet since Comcast's takeover.
While as I said I do like the idea of a 30 Rock treatment the facades are supposed to get, is just putting something in because it's more popular NOW a good reason for an attraction? Basing an attraction off of a real-life person is just an odd choice to me.
Although Martin Short's Making of Me video was well worth the time.
The Tonight Show itself has been popular for over 60 years. It's an iconic brand. So I think building an attraction/facade based on it is a safe bet.
I agree, though, that in the unlikely event that Fallon flops as host and is replaced (unlikely because his ratings right now are very good- almost 4 million viewers a night), the attraction would then be a bust and would need to be changed or replaced.
But "The Tonight Show" franchise will likely continue long after Fallon is fired or retires.