SiloeSid
It appears that you are confusing free calling flying low level where free calling a general frequency is not uncommon with flying high level in IFR where you are under mandatory control. Just dropping off a controller's frequency and onto another is not an IFR procedure. If a pilot is concerned that it is time for handoff then by all means call the current controller and just ask when can we expect handoff to [
name of next agency] it might annoy the controller but should get a response. If the pilot feels that radio contact has been lost as it has all gone quiet and nobody replies then that is what 121.5 is actually for. As you are in mandatory IFR airspace and you may be in conflict with other aircraft it would also be an idea to squawk 7600. To get out-of-range of a control frequency is quite difficult at high level unless you have flown a considerable distance and not bothered to maintain situational awareness, which appears to be the case with the BA aircraft in this post. All frequencies have multiple transmitter stations and can be expected to provide cover tens of miles beyond the sector boundaries.
You should also remember that there is a standard handover/assume procedure between all sectors. The receiving sector can see an aircraft coming toward the sector airspace with a datablock that tells the controller all the pertinent details about the flight. A sector controller will not sit there quiet while a flight under the control of the 'upstream' sector bores into the sector airspace. The controllers will be talking between each other about the flight trying to work out why it is not responding and being handed over. Do not assume that just because nothing is transmitted on radio there are no discussions taking place. The normal handoffs are silent using the computer systems to transfer 'control authority' over the aircraft. If in the middle of this process you waltz off to a different frequency the controllers will not be best pleased especially if there is some deconfliction to do immediately you are assumed by the next controller. Delay could easily be due to a lot of coordination of other traffic not on your frequency.
See
https://www.youtube.com/watch?v=dYYHR_G7Res
Do not confuse low level VFR procedures with high level procedures in mandatory IFR airspace.
