What does the remote-actor framework do if trying to write to a client which is no longer there?

I have a server which is using the remote actors framework to communicate with multiple clients. As mentioned in this question, I am having trouble keeping track of when a client disappears. Hence my server is still attempting to send messages to non-existent clients.

• Is this a problem? (I don't see any exceptions being thrown - but I assume there'll be memory issues if my server is long-lived)
• How can I detect that a message is being sent to a client no longer listening? (If I want to implement some kind of connection clean-up)