When the seals fail on the slave cylinder it creates so much drag that the cylinder won't move even with the full weight of the pressure plate springs trying to force it to return. I was informed of this by the Tech at my dealer, he tried to get the slave piston to move by hand and didn't have the hand strength to move it at all. I can also state that after having mine replaced under warranty the pedal pressure was noticeably lighter that it was before the slave cylinder started sticking. So if we were to fabricates some type of force measuring instrument we could probably test the pedal pressure on a weekly basis and know if the slave cylinder is starting to fail.
Personally I've started doing something I loathe doing to try and preserve the slave cylinder, that is putting the car in neutral when stopped at a light and releasing the clutch. It means that I will have a delay if I need to dodge a rear end collision but I drive in so much traffic that being first at a light is rather rare.
PS; I've been tinkering with hotted up cars since the late 60's. Performance parts are designed for one purpose and one purpose only, that is to exceed the performance of OEM parts for a short period of time. Which means that a performance will launch harder and won't slip under much higher power levels but it won't last nearly as long as the OEM part. If you want to race your car, get performance parts. However if you want to drive your car as a daily driver, the do NOT use performance parts unless you have the funds to replace those parts every racing season or even every half season. This is especially true for brake pads. Because racing pads are designed to function best when they are really HOT. As a result the stopping power on the "street" is pretty miserable, they will either lack in braking power when cold or can be quite grabby.