After putting all the config under version control, I can confirm, that wifisetup -killap will simply remove the wifi-iface as shown by the following difff:
diff --git a/wireless b/wireless
index f5bfbb3..b24bc29 100644
--- a/wireless
+++ b/wireless
@@ -9,13 +9,6 @@ config wifi-device 'radio0'
option txpower '30'
option country 'US'
-config wifi-iface
- option device 'radio0'
- option network 'wlan'
- option mode 'ap'
- option encryption 'none'
- option ssid 'Omega-XXXX'
-
config wifi-iface
option device 'radio0'
option mode 'sta'