Does the 2008 XF 2.7D have a rear brake pad level sensor?

Just been quoted a price to include rear sensors but NEVER ever had a sensor warning...

 

I don't think it does, but it's very easy to check yourself.
Just whip the RHR wheel off and have a look for a cable running from up in the top of the wheel well down to the top of the inner brake pad. No cable = no brake pad wear sensor.
There are only two brake pad wear sensors on the XF, one on each of the RHR and LHF inner brake pads. They are quite cheap, around 10 GBP each, so don't get ripped off paying for them and especially non-existent ones.