The biggest risk I see in regards to @steemit's stake is that it could get sold to a bad actor that may not hold the Steem community in high esteem i.e. Mark Zuckerberg or something like that.

As for whether or not they should Power Down, it's a tough call, I cannot imagine what I would do if I was in their shoes.

Hopefully there will be a compromise i.e. some of their stake is placed in a community trust, and their remaining Steem is used to profit their shareholders.