[x] Stay until the breach is secure, likely expending more chakra but also reducing Sandayū's casualties.
Most of our chakra expenditure came from the 30 seconds of guarding the samurai, rather than the fighting afterwards. (Base 20 chakra per second for 30 seconds with a 90% chakra reduction =90% of 600=60 used). Combat against low level forces won't be nothing, but it's only the higher ranking or continuous techniques that burn through Hisana's chakra. In terms of rough percentages, the initial approach was 18%, of total chakra, and another 2% for the combat that followed. Feel free to correct me if you don't like my maths.