Very unlikely it got shredded into bits. Usually a fish gets sick and then sticks to the grill on power heads, occasionally making a bad choice and getting stuck to the grill.
If it didn't jump out of the tank, it is more likely to be under some rocks in process of being consumed by bristle worms in the back of the tank, etc. Always sad to lose a fish, so my heartfelt condolences for that.
As for the white organisms, are they moving?
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