Here are a few of the responses:
- Either create a fully covering blast of particles and fade to original or use Blobbylize instead, with Particle Systems II or such and fade in a solid alpha [from Jens @ Cycore]
- try precomposing your sequence and then just reverse your precomped animation.
- yes play it backwards. And do a crossfade. See the old case study... by Chris Meyer from 1998 [Chris and Trish have a ton of stuff buried at PVC]
- if you animate the blob birth and death sizes from small to well past the slider range of 2 to something like 5.4 for death size, the blobs go to form the original image.