Kudos for not saying 'a good friend of mine has overstayed'
This was about 3 years ago, so many things may have changed. But i did meet a chap in a similar mess to yourself, though many less years at the british embassy. from his experaince I would say that nobody can tell you wants going to happen because that is at the mercy of so many individuals at the embassy, immigration, the courts and the airline. if they all decide to make things easy for there's nothing to it and if one of them decided to make it hard, then its gets unpleasant real quick.
If you are a brit, the embassy isn't going to help you with money... your on your own. what they can do if they think your a 'deserving case' is intercede with immigration when you do not have quite enough money to buy the ticket and flight. by deserving, still having your passport is a major plus, if you don't they assume you sold it and that puts you quarry in the feckless category.
ij this chaps case they interceded with immigration and immigration decided on a fine he could pay after he bought his ticket home off them. he went down to immigration, paid for the ticket and was bailed until his court appearance the day before the flight.
on the day, he went to court, paid his fine and shipped to the IDC for the night. on the way the van stopped and they were let out for refreshments offered by the drivers (can of coke being 100B). When they got to the IDC they were all initially kelt in a meeting room for the night.... until senior officer came of site, for whom they were put into the IDC proper. A rather horrid, place you never want to be in, where the images are very interested in having your phone and cash should you have any.
you will be taken to the airport for your flight, you will be kept in a room until you are about to board the plane. the planes captain has to be asked if he will carry you, a conivted criminal being deported, he has the right to say no even when you ticket says yes... if your are european air india is popular, if you are african you might be waiting 5 years for a plane to take you home
The chap flew with air india, he did not get his travel documents until the last flight in the itinerary and when he arrived at the connecting airport. he was detained by the police and marched to his connecting flight .
at heathrow he was collected at the plane door by uk police, and taken though the tunnels of lhr. he was processed into the country and dumped on the curb Heathrow, to make his own way to where ever he needed to be.
As for blacklisting, he was not. but that was before they anointed the blacklisting rules for overstays.
Personally, I would suggest that you have a chat with your embassy and see what your options are. paying the fine at the airport and leaving is a much better option of going to court... but then with a 10 year overstay, they would probably have the option of running your day by sending your to court rather than the plane.
Best of luck and try not to do it again