This is more a rule of thumb for the receiver; if you send a transaction (based on coins which are already well-confirmed), and don't try to send any conflictin

This is more a rule of thumb for the receiver; if you send a transaction (based on coins which are already well-confirmed), and don't try to send any conflicting transactions, then it shouldn't disappear as long as it gets one confirmation (even if the block chain forks, it will be resubmitted)