Q5 is a reverse charger protection FET. If SYSP and SYSN is connected backwards, this FET will turn on which makes Q2 turn off and disconnect the charger from battery/IC. The diodes D9 and D7 on the DIS and PCKP pins protect the IC from damage by diverting the current through external low Vf diodes instead of body diodes in the IC.
Backward charger connection is a problem for cells because it will discharge the battery at whatever rate it wants. In case the customer has mechanical or other techniques to guarantee that the charger can never be connected backwards, then the Q5 FET, R25, D7, D9 can be removed.