Reddit will die off in stages. Slowly.
First the power users are leaving now. These are the mods and the major content creators (think Minecraft leaving)
Eventually they will piss people off again and the more common content creators will leave.
Then after reddit has worse and worse content, the users who just comment will leave.
After that there will be nothing worthwhile for the lurkers and they will leave too.
Reddit will then be a wasteland.
This will all take quite a while. Even Digg took time to die off.