All right--the fairest method I can find, then, is that a player will be marked as Frozen and can be attacked as normal. Additionally, they will regenerate HP as normal, but collect half coins.
In order to maintain balance, a player may opt to not attack anybody on a given day. If a player does so, they will not attack anybody (but can be attacked), will regenerate HP as normal, and collect half coins (as if they hadn't fought anybody anyway).
As busy as I am today, the post probably won't make it up. This change is effective immediately, so feel free to change your target if you want.