As someone who is a massive fan of the Grunge/altenative-rock movement of the '90s, this is a topic which greatly interests me! I quite often think about "alternative" (unintended pun) scenarios, so it's interesting to discuss how Grunge/alternative-rock would have panned out if Nirvana had never existed.
Even if Nirvana had never existed, i'm almost certain that the alternative-rock movement still would have emerged in the mainstream. The reason why Grunge/alternative-rock was so influential in the first place, is because it was the product of a demographic which was gaining power and influence. Grunge reflects the social values and world view of the collective Generation-X. There was evidently a backlash forming against the materialistic '80s and people wanted something more authentic.
I have my doubts that Pearl Jam would have led the alt-rock movement, in such a scenario.
Ten only became a breakthrough success in the second half of 1992, despite the fact that the album was released almost a year earlier. Initial record sales for the album were quite low. I'm not sure if there would have been a band that would have led the movement to the same extent as Nirvana did, to be honest. I even have my doubts over how successful Soundgarden and Alice in Chains would have been.
Badmotherfinger only peaked at #39 on the Billboard Album Chart and none of the singles peaked on the Billboard charts. Their success was largely as a result of Nirvana's breakthrough into the mainstream.
If any band were to lead an "alternative" movement of some kind, I believe it would have been Metallica. Their self-titled album was a huge, worldwide success back in 1991 and they were very successful throughout the '90s. I personally don't think a different movement would have formed as a result of Nirvana's absence. In any case, Grunge still would have been a popular underground movement in the Late '80s/Early '90s, and it likely would have emerged into the mainstream at some point. It just wouldn't have been as influential.
Regardless of the trajectory of alternative-rock, Glam Metal still would have fallen out of favour around the same time, in my opinion. Glam Metal was in a similar state to what Post-Grunge was in the Late 2000s/very Early 2010s. It was still popular, but it was on the decline. Like I mentioned in the second paragraph, it was a generational change which partly resulted in the mainstream breakthrough of Grunge. Glam Metal was on the wane and I believe it's very unlikely that it would have survived into the Mid '90s.
I don't think there would have been a '90s "Emo" movement. The public was very embracing of alternative music in the '90s, so if there was any real chance of "Emo" breaking into the mainstream, it likely would have surfaced in the mainstream sometime in the '90s, even with the popularity of Grunge.
The absence of Nirvana and the change in trajectory of alternative-rock, would have had a significant influence on '90s and 2000s music. I personally believe Post-Grunge would have died out in 1999/2000, in such a scenario. The reason why Post-Grunge lasted for as long as it did, is because of how influential the Grunge scene was and Nirvana were mostly responsible for that. Had Nirvana not existed, the alternative-rock movement likely wouldn't have been as influential. That means bands such as Creed, Nickelback and Puddle of Mudd would either be unheard of or simply wouldn't exist.
As a result, it's possible that Emo would have had more of a presence on the charts during the 2000s, due to the absence of "post" Post-Grunge. Of course, that also puts into question how long Emo music would have lasted in the mainstream. Due to the possibility of the genre "peaking" earlier, there's a likelihood that it would have been phased out sometime in the Late 2000s, possibly around the time Electro-pop emerged.
It would have been interesting to see how alternative-rock would have played out in Australia. My reasoning for pinpointing Australia, in particular, is because the country had a Grunge/alternative-rock movement of it's own and it was just as influential in it's own right. Our Grunge/alt-rock scene also began in the underground in the Mid 1980s and there's even debate over whether Australia can lay claim to being the country that invented Grunge. Kurt Cobain acknowledged that the Australian Grunge movement had an influence on him.
The story of the alt-rock movement in Australia is unique, in that it actually emerged in the mainstream earlier than it did in America. The breakthrough of the genre in Australia was similar to Nirvana's emergence. Ratcat, an underground band from Sydney, was responsible for the breakthrough of alternative-rock here. Their debut EP was only expected to sell 5,000 copies, but it sold over 100,000 copies. It constantly went out of print.
"That Ain't Bad" and
"Don't Go Now" both topped the charts, the former finishing as the second-highest selling single of 1991. Anyway, if Nirvana never existed, I think Ratcat would have continued to lead the alt-rock movement in the following years, especially seeing as though they were the "lead" band for most of 1991.
RockyMountainExtreme You seem to be a fan of '90s alt-rock as much as I am. I would highly recommend listening to a few Australian Grunge/alternative-rock songs from the '90s. Of course, Silverchair were the most internationally acclaimed alt-rock act from the country, but there was so much more to the movement and a lot of it is really good. I could suggest a few songs, if you're interested.