I’ve had two slave cylinders fail, the first did as yours has done, pedal to the floor, one day fine, next day stra to the floor, no warning. The second failed differently in that the pedal returned but only half way and needed flicking up, but only sometime, other times depressing the clutch pedal disengaged the clutch but after a second or so it would re engage with no pedal movement, which made life interesting.
The original slave cylinder had a plastic body, the second was the same, fortunately (?) it failed after 2 months and 1500 miles, (so under warranty) and its replacement was metal bodied despite the kit having the same part number.
It would be worth getting the DMF checked to see if that needs replacement at the same time.