QDM -
Totally agree - hence my comment that the (second) decision to turn back to the airfield behind me was probably the best flying decision I'll make.
In hindsight - would I have done differently? Hell yes, if I'd thought the cylinder would fall off I'd have never taken off again after taxying off to the ramp. The initial rough-running was distinctly like plug-fouling, and I suspected that the problem would quickly clear. After a number of touch-and-go's I'd had spark plug fouling before a couple of times (I guess this is a possible symptom of the 'power-on', 'power-off' nature of circuits). This occasion - at first anyway - seemed pretty much the same, so my first thought was "that's enough touch and go's - I'll get the engine properly warmed and clear the plugs, if that is what's causing it". So you could say that in hindsight this was the wrong decision, yes, because plug-fouling it most certainly wasn't.
When it became very apparent that the problem was more serious, I had no hesitation in heading for the nearest mile of tarmac - i.e. immediately behind me.
It taught me a lesson - be aware of the 'sound and feel' of the engine and be wary of any changes, whether sudden or otherwise. The other lesson might be to strap skis, floats, wheels and a parachute to the plane, to give a fighting chance in the event of engine failure, but this would make for an interesting weight and balance calculation...