Even if all turns out to be some kind of big misunderstanding in the end: a service holding bitcoins in the tens or even hundreds of thousands of bitcoins for thousands of users simply cannot be left unattended for a period of three days. If nothing else, the owners of mybitcoin are unprofessional and careless, which invalidates their service for further use.
Yeah, 8 hours is too long for a service this size to be without communication... anyone still holding out hope they'll come back might as well hope for the second coming of jesus instead.
Online "companies" are the same as missing kids - if you don't hear anything in 48 hours, start the grieving process.