o2 sensor

[twiceasspeedy]

Having taken the airbox cover off to fix my little tps reset problem (thanks again for the help btw) I noticed that the previous owner had disconnected the o2 sensor, I recall him mentioning something about this along the lines of, because it has a custom exhaust with a custom tune, he didn't want the o2 sensor messing with the custom tune. It has been this way for about 3 years apparently (I have had the bike 2 weeks, and it runs great with no issues, except for the ECL coming on, which he told me was because it wasn't stock anymore, i.e the exhaust valve is disconnected along with the o2 sensor, disabling the active exhaust in ecmspy along with the o2 warnings has turned light off, as these were the only error codes it was throwing.)

Now I realise that the ecu was giving the 'o2 sensor inactive' code for a reason (code 13 from memory), and turning off the warnings for it is not addressing the 'problem' at all, so my question/concern is this: How does disconnecting the o2 sensor affect the stability of the bike, in terms of engine wear etc? I mean will the bike 'explode' one day with little/no warning? Should I reconnect the sensor? If I do what are the likely outcomes in terms of my custom engine maps etc?

Thanks in advance for your thoughts/ideas guys.

(Bike is a 2007 xb12 lightning long with 22,000km (~13,600mi) on the clock)