I would assume that an RPG-style jelly dies when it is no longer able to maintain the surface tension that defines it as a creature. As such, I imagine an RPG jelly is somewhat like a water balloon, and can die in two ways:
-Evenly distributed loss of surface tension (eg, the jelly melts smoothly into a puddle)
-Catastrophic loss of surface tension (eg, the surface tension suffers a perforation and external pressure destroys the rest of the membrane)
Considering that most RPG jellys are low level, and therefore smote by physical impact, the latter is more likely.
Ostensibly, the reason your death animation looks off is because the creature loses volume in the middle of the frame, only to regain it as it becomes a puddle. Perhaps a case study of my earlier comparison would be useful.
This has the most impressive aesthetic, I think, though
this is probably more relevant (on a flat surface).
The walk animation is very cute, by the way. It has a lot of personality.