I bought a Varilight dimmer about a year ago to control a fitting in my
study which has 4 x 50 watt GU10 bulbs. I can control it by remote from my
desk.

Today the lights went out - I put them back on and found they went out after
about 5 seconds when on full - longer when dimmed. Tried removing a couple
of bulbs - slight improvement.

Is it dying? Is this how they fail?

I understand this type of dimmer is best at withstanding the effect of a
bulb failure - this is why I bought it in preference to a conventional
dimmer .