inQuiescent Current with Downsteam Devices
When the TPS61098 is in "Low Power Mode" and drawing only 300nA of quiescent current, there will not be an output voltage on your Vout rail. If you look at the datasheet, it shows "No load, No Switching", meaning that your Vout will not be supplying any voltage. Therefore, you shouldn't be seeing any leakage current downstream since there's no current to draw to bein with.