“Presumed Dead” Characters Actually Alive But Audience Knows the Whole Time

[Liberty City]

2007: On The Young and the Restless, Nick was presumed dead in a plane crash; in reality, he was left stranded from the wreckage.

[Cruising Soaps]

I think the best one in Daytime was...

Y&R/B&B

Sheila's first crossover to B&B.  Everyone in Genoa City thought she was dead, but was hanging out in Los Angeles causing havoc there.