Too early to tell whther this solved my problem but recording for posterity anyway. In theory this will stop my Raspberry Pi from dropping off the network after it has been idle for a while.
pi@dashboard ~ $ iwconfig
wlan0 IEEE 802.11bgn ESSID:"Professor Ping"
Mode:Managed Frequency:2.437 GHz Access Point: B8:E6:25:9B:62:02
Bit Rate=39 Mb/s Tx-Power=20 dBm
Retry long limit:7 RTS thr:off Fragment thr:off