All dApps will need to cover their staff and server costs.
Musing does not publish posts for author rewards nor take a beneficiary cut. So their only Steem-based revenue stream will be curation rewards which are paid in 100% Steem Power.
If Musing are trying to cover their costs using the Steem economy they will thus need to power down.
The good news is that the 1m Steem Power delegation from misterdelegation does not form part of this power down, so rewards are (almost totally) unaffected.