HI there.
First thing how often do you check your gear lever for tightness, I will check it a lot more often after today. It was a lovely day here in North East England for a run, so I set off for a run down to the coast only about 10-12 miles got there no bother continued on further down down the coast then cut back inland over to the A1 and headed back home got to my turn off slip road which is uphill to traffic lights which were on red, went to change down only to find gear lever missing had to stop at the lights, but because of incline could not pull away in top tried but engine stalled holding in the clutch pushed the bike round the roundabout off the opposite slip road onto a housing estate. Thankfully I was only about a mile from home but there was no way I was going to be able to push the bike up the very steep hill home so rang the son who arrived after just a few minutes during which I had a plan which was go home with the son in his car take the gear lever off the A65 which was in the garage go back fasten on and hey presto drive home. Soon as I looked at the lever on the A65 I knew it would not fit smaller spindle so plan B took a set of Mole Grips down clamped to the spindle changed into nuetral started the engine and using the grips changed into second gear pulled away and drove the mile home. I do have breakdown cover which I would have used if I were any distance away but I reckoned that I would have been home before they could have got to me. Why did it come off I have not had the gear lever off for at least 6-7 years and used the bike every year. Ordered a new lever on Ebay will check it now on a regular basis.