This was a civilian rather than private flight carrying 72 PAX. It is easy in CAS to take down the wrong frequency for the next transfer.
Normally you write the frequencies down or at worst keep the previous frequency incase you need to flip back to get a confirmation.
Failing that there is always London or Scottish info to help and numerous other options.
Other than radio failure its hard to understand why a commercial flight should be out of communication for so long ?
Pace