I definitely think there is a risk. However, reddit is much larger now than Digg was then. And reddit existed as a clear alternative to Digg at the time of the redesign.
I think there's a very real risk of a redesign going wrong, but it may be large enough and better enough than alternatives to weather the storm.
"Better enough" is a funny thing when it comes to redesigns, because all the previous routes to value that are ingrained into your brain are now gone, or look funny/different. Thats why I predict a brain drain as people pick up and realize it really doesn't do much for them anymore.
I think there's a very real risk of a redesign going wrong, but it may be large enough and better enough than alternatives to weather the storm.