No if the heat pad gets too hat it shuts off. All t-stats do this the herpstats (duals zone models) will also shut off if the temp drops too low rather than continuing to heat the enclosure. All the others (as far as I know) require a fail safe to protect against over heating the enclosure if the probe is accidentally removed from the heat.

The mechanical relay is naturally closed the electronics keep it open any failure in the control board will cause the relay to close. It should in theory fail closed not open. most triac controllers have at the very least an equal chance of failing open (heating or closed no heating) the new herpstats are more likely to fail and go cold rather than run the power maxed out. Again making a failsafe questionable. For myself I will NEVER run a T-stat that had a good chance of failing on and un regulated or if the probe being pulled free by accident meant the likely injury or death or anything it was regulating with out a fail safe in place.

For my personal piece of mind a failsafe is not optional and the only time I would question the absolute necessity of it is the newer herpstats as the features make it many times less likely to ever run maxed out uncontrolled.