iOS and OS X had Reeder back then, which used Google Reader as an engine and then released a new version that stored the data locally. That's how I primarily used Google Reader back then because the user experience was so good. For other platforms, five-year-old Feedly was very mature and the platform I'm using today since I left Apple (Feedly Classic to be specific since they made their "new" app awful).

To summarize, yes. There were plenty of mature alternatives and a migration was easily done by exporting and importing a file. Feedly supposedly got 3 million new users in the two weeks that followed Google's shutdown.

A far bigger issue than Google shutting down was the fact that people had moved on to Facebook and Twitter while newspapers created closed ecosystems with their own apps. Jason Kottke, then one of the world's most popular blogs, declared blogs to be dead.

The issue isn't "are the available now", it's were they practically available at the time reader was killed. At the time reader was killed there were a plethora of okay-ish options, but most were new, or lacked the usability polish, or lacked the perfect syncing of reader. As a result when it was killed for the majority of users there were no practical alternatives: new projects weren't an option for most users because they lacked the usability polish, and obviously a brand new project with few users doesn't instill a sense it won't go away shortly (especially given the context). Plenty of apps existed but many of them used reader for syncing (womp womp), and those that didn't required you pay or required you have some other paid service for syncing, and still because they were apps you couldn't just use them wherever you were (plenty of work computers limit software installation etc), browser based ones require you use the same browser everywhere (and required you to not use chrome because it doesn't have integrated rss, and so you run into the chrome monoculture of web devs forcing use of chrome, and corporate software installation limits preventing firefox), and plenty of the OSS ones required you literally run your own server (which is what I've been doing for years), or rely on random 3rd parties who may or may not be able to afford a free service indefinitely. (holy run on sentence batman)

The result of this was when reader shutdown the overwhelming majority of users simply stopped using rss, presumably even if they did export their subscriptions they've long since lost them, and built up habits around non-rss based mechanisms. Hence rss (for anything other than podcasts) ceased being relevant for the overwhelming majority of people.

I'm trying to make it clear here, the issue isn't that using RSS became impossible, it's that by making reader free google decimated the rss reader ecosystem such that when they killed reader there simply weren't practical alternatives for the majority of users of google reader. As a result reader being killed changed the general habits of those users to no longer use rss feeds for information, and given by that time things like twitter provided similar services (most blogging platforms have a "post updates to twitter") they had no real reason to go back to rss readers.

So the basic argument for reader making rss become irrelevant for general blogging, etc was:

1. RSS comes into existence

2. Apps start being made to subscribe to rss

3. People start using those apps

4. Google introduces Reader, which is free

5. Paid apps from <2> can't compete with free so either die or adopt in app ads (which at the time reader didn't have) so people move to reader

6. Non-google rss readers don't have syncing, so people move to reader

7. Non-google rss readers either require people pay, or use specific paid services, to get syncing, so people move to reader. Or they use google reader as their back end so their users can now trivially just start using reader anyway.

8. At this point there are no major alternatives to google reader, it makes up the overwhelming majority of all people using rss, as a result the few stand alone readers that still exist are for niche use cases or are unpolished hobby projects that come and go over time

9. Blogging platforms introduce tools to allow posts to blogs to automatically post updates to twitter, Facebook, etc

10. Google kills reader

11. The free rss readers that still exist all use reader for syncing, so lose syncing, and have to either charge money or require users adopt paid syncing tools, so people don't migrate to them. The projects that come into existence at this point are too rough for general users so they don't bother, and at this point they don't need to as the autoposting from <9> means that they don't need it.

I think that's a fairly fair assessment of what happened. But I think there's a big caveat to be addressed though. Google reader was far and away the most popular RSS reader, like overwhelmingly so, prior to it existing the market of RSS readers was something where a few people could earn some money, but it was not really a significant market. So my question is, absent google reader would RSS feeds ever have become as popular as they were during the period reader was available?

My _feeling_ is no.