By certain type of cancer, mutations are well known. Genome/epigenome editing could possibly "repair" such genes or silence them by methylation of their promoter.
In my opinion, owing to the vastness of the genetic and epigenetic alterations in cancer the only way forward is to get rid of the mutated cells. Genome editing of immune cells could help achieve this but I don't think we will ever be able to revert the actual cancer cells back to their former 'healthy' state.
I think one of the actual bottleneck for such repair for cancer cells is delivery of those genome/epigenome editors. It's hard to precise delivery in vivo and impossible to achieve 100% precise edit in every cancer cells.
Due to the hard mission above, kill them is a more direct way.
I agree with you. For the non solid tumor is it conceivable to target the tumor cells with a specific antibody (the RNA and nuclease would be linked to the antibody)