Zabbix can store active item values for a specific time (max 3600sec) or for a specific size (65535 values). In case of network issue that can last more than 1 hour or in case of buffersize overloaded, all values are lost.
For customer, losing values cannot be acceptable and zabbix agent should be completly autonomus until issue is resolved.
What could be interested is to store all value in a buffer file (no limit), and zabbix agent will send buffer file content when connexion is establish again.