We need to introduce `reinvokeNeeded()` logic back in some form. 

Backup ops are sent by owner nodes to backup nodes after operation is executed. Then owner node sends operation response to the caller. Then backup nodes send backup responses to the caller. 

In case when owner node (`target` here) dies after response is received;
- if caller gets backup responses in some time (5 secs here), then everything is ok
- but if not, then caller should re-invoke the operation from scratch