Could have been nasty.
If the tyres were 'going off', why the hell didn't you go straight into the pits!??
No, going off (in this instance) just means they are just losing about 1% at most of the grip you had a couple of laps before.
In fact I have just analysed the cause of the slide. The driver generally did a very light brake here, hardly anything at all but it resulted in a turn-in speed 3.5mph slower on the previous laps. So, he went in 3.5mph faster, not a huge problem in itself but he must have felt this, been slightly nervous of turn-in and so turned very slightly less meaning that when he got to the apex he had to add a 'little' bit more lock (you can easily see it). Also, normally he would have been on full power before the apex and hence have moved x% weight to the rear, going in a little faster and that bit of (sub-conscious) nervousness meant he didnt have full power on, instead just balanced or maybe slightly positive so, a combination of all these things led to the oversteer.
In fact the car was travelling 6mph slower than 3 of the previous 5 laps at the moment that it 'let go' (the other 2 were an out lap and a traffic lap) so it wasn't speed at the exit.
The tyres were getting past their best but in the next session we were matching the same exit speeds with no bother. Apex speed in these later sessions where only down 1mph on previous 'best sector' speeds.
Maxx