Car is just over 2 yrs old, done 20000 miles.

I was driving out of a car park at the weekend and this light (yellow engine symbol) came on with a beep along with the generic warning light (yellow triangle with exclamation mark). I stopped and checked fluid levels etc. Also got the warning that "start stop" was disabled All appeared to be OK and the car appeared to drive normally with no misfire etc. Booked it in to the garage for diagnostics next week, they said OK to drive until then. Have used it 4 times since then, car driving OK. Filled up with petrol (was half full at that point) and now the warning lights have gone off. I guess the garage will be able to get the stored fault codes, but is it still worth going and paying to get the diagnostics done, as everything seems OK?

On a slightly separate point wouldn't it be useful if the fault codes flashed up on car dashboards in a situation like this to save a lot of hassle so the significance of the fault can be quickly indicated and reported to the garage who could then give a more informed opinion of whether it was OK to drive?