Die hard is a 7-cell methuselah (essentially a collision between a block and the traffic light sequence) that vanishes after 130 generations, which is conjectured to be the limit for vanishing patterns of 7 or fewer cells. Note that there is no limit for higher numbers of cells, as eight cells suffice to have a glider heading towards an arbitrarily distant blinker or pre-block.
"Die hard" as a general term
Alternatively, "die hard" or "diehard" may refer to any methuselah that eventually vanishes. Soups in Conway's Game of Life lasting at least 500 generations before disappearing completely are reported by apgsearch versions v4.69 and above and referred to as "messless methuselahs" on Catagolue.
As of 2020, the longest-lasting diehard found fitting inside a 16×16 bounding box lasts 1279 ticks and was found by goldenratio on December 18, 2020, based on a 1277-tick C1 soup found by Rob Liston on February 3, 2020. The longest-lasting symmetric diehard (fitting inside a 32×32 bounding box) is a 1760-tick C4_4 soup found by Moth Wingthane on January 27, 2020.
In other rules
In HighLife, despite the instability of the traffic light sequence, the die hard still works, disappearing after 119 generations.