Knowing that Network MIDI is in its first official specification release in MIDI 2.0, it is primarily focused with a peer-to-peer connection between devices, and likely that will tend to be a 1->1 relationship between client and host, although the spec does support multiple client connections to a host, including from a single device.  The specification mentions the ability for a client to essentially determine that a host is not available after a "reasonable amount of time" when submitting repeated Invitation packets (Network MIDI 2.0 Section 6.4), but is there an equivalent concept of the host determining that a client is no longer reachable, in case the device has been powered off, or otherwise removed from the network before sending a Bye packet?  For a host process that might want to only accept a certain number of client connections, such a timeout strategy would help to free up a connection for a client that is no longer active.  I am unable to find any discussion of this within the Network MIDI 2.0 specification.