Occasionally Connected Client
The commands applied locally on client to produce events. When system comes back online, the persistent subscription pushes the unseen events to the client. The client/domain model can inspect these events and see if they conflict.
The commands are stored in a local file queue.
We know what events these commands will produce - as such we can walk the queue back down and see what command caused the events which conflicts with what we got from the persistent subscription. Then the GUI could ask the user what to do with the command, whether to change it, throw it away or overwrite "existing events" with that command.