An interesting and good account.
Without intending to detract at all from the spirit in which your account was written I think Foxmouth makes a good point.
With hindsight it is easy to say, but with zones like solent if you dont get the clearance you are expecting it is well worth having an avoid plan up your sleeve which then becomes second nature even if you are still worrying about an earlier problem. With solent for example their are several ways around or through the zone which do not require a clearance.
Also it is worth looking around for smaller airports that are often not as busy and more likely to take on the repsonsibility of signing you off with the earlier unit. In this case what about Goodwood Chichester that are always worth a call for a FIS when routing along the coast.
Finally, and happy to be corrected, but because an aircraft does not sign off with a unit and given the unit has no obvious reason to believe a problem has occurred I cant imagine a SAR action is a high priority for them so their is plenty of time on your side to ask another unit along the route to pass the message - any will do.