If a stolen iPhone was in airplane mode will a find my iPhone passcode lock apply itself when the hone is switched off of airplane mode?

My girlfriend's iPhone was stolen whilst on holiday in London. The phone was in airplane mode and didn't appear on Find My IPhone, which was installed and enabled (all set tis correct other than airplane mode). I sent a remote passcode lock to the phone.

The next day the iPhone appeared on the map, obviously having been switched on and had airplane mode switched off. My question is, will the remote lock apply immediately the phone comes back online?

I assume their only opting at that point is to do a factory restore which would wipe all the data anyway, right?

Also, can't Apple track the IMEI number regardless of a restore and a new SIM? Or the network operator that the phone was originally connected to?