Won't matter. There's no real lock-in among text / link content communities. They're trivial to build, there will never be a lack of new variations. Reddit doesn't even have possession of the vast media (youtube, imgur) that gets posted to its service, making it that much easier to replace.
Imgur will probably see among the greatest benefit as Reddit erodes.
That's true about Imgur. It has already gained a sizable community not directly related to reddit before this fiasco, I wouldn't be surprised if it grew more quickly now. It has the infrastructure as well as the most popular form of content from reddit - unlike something like voat.
Right, the critical difference between Reddit and Imgur - Imgur contains the content. They're the host, rather than sending traffic off-platform. Just like eg YouTube. Those types of platforms end up being vastly more valuable; if you don't own or control anything on your own site, it'll always come back to bite you. Imagine Facebook hosting all of its photos on another site like Imgur.
With Reddit's approach, you end up creating lots of competitors; given the right context, or given enough time, those competitors will bleed you out. Twitter figured that out with TwitPic et al.
Imgur will probably see among the greatest benefit as Reddit erodes.