Assuming there exists a malicious entity, they have managed to own 51% hash power, and executed a sustained 51% attack on Bitcoin, say 24 hours. In this case :
- What are the options then to recover from it ? Is there a hard fork necessary and how long it could take practically for miners ?
- I see some comments suggesting consensus algorithm can be updated. Is there any algorithm fix that can be made to prevent or prepare against 51% attack ?