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.