I am releasing a new bugfix update to Google Play. I have been trying to nail down the reason of the worlds disappearing after updating. This upcoming update changes the application bundle format back to the old style, as used by 2.3 and earlier – maybe that will help.
If it works, the people who have not yet updated will not lose their worlds. On the other hand, those who have already updated might have their worlds wiped again.
I don’t know whether it will work or not.
Please backup any valuable worlds before doing updates on Google Play until this is sorted.