The questions raised are a bit of a tall order for a few lines, but here goes: -
1) Coal was (and in some cases still is) mined throughout the different coalfields within the UK, and began at least as early as Roman times. There are many coalfields of differing sizes throughout the UK, e.g. Nottinghamshire, Derbyshire and South Yorkshire, South Wales, North East, Scottish Lowlands, Staffordshire, North Wales, Cumbria, Lancashire, Forest of Dean, South Derbyshire and Leicestershire etc. Different coalfields could have different types and qualities of coals which were highly sought after e.g. South Wales - anthracite, Durham - coking coals, Nottinghamshire, Derbyshire and South Yorkshire - general purpose coals etc.
Coal was first mined on the "exposed" coalfield where the coal bearing rock sequences (the "coal measures" - sandstones, shales, clays, binds, cannels etc. - and the coal itself ) where they were at the surface and directly below. An exposed seam is known as an "outcrop". As demand increased, further coal was mined within the "concealed" coalfield, meaning different, newer rock types lay on top of the coal measures. This also meant that mines on the concealed coalfield tended to be deeper and more recently constructed - however some mines in the exposed coalfield could be very deep too.
2) Coal production peaked in the first half of the 20th Century, and was related to developments brought about by industry, mechanisation, and the war effort. Coal had fuelled the industrial revolution, and Britain as an industrial nation was" built" on coal. It first replaced wood and charcoal in the industrial processes of the 18th Century at places particularly Coalbrookdale.
3) There are many reasons for coal's demise in recent years. From the 1950s onwards there was a natural decline as coal reserves diminished, and the remainder became more difficult to work. This was followed by competition from nuclear power, and cheaper oil and gas for coal's main market of electrical power generation. Most of the industrial processes using coal were also in decline. The Clean Air Act meant that both the domestic heating market and industry drastically changed, and the railways moved to diesel and electrically powered locomotives - mainly related to pollution concerns.
There was also a major political element to the "Fall of King Coal". The mining unions held incredible power, and could hold the country to ransom, as they did in the 1970s. The Conservative Party, later to become the Conservative Government under Margaret Thatcher resolved to break all union power, and this meant the NUM. Plans were put in place by the government over many years for this fight. For the NUM it was about jobs, livelihoods and communities. Mrs. Thatcher said it was pure economics. By 1985 the Government won the fight after a year of strike and bitter struggle, and sure enough the pits started shutting immediately. 200 before the strike and around 12 today. 200,000 jobs before the strike, and around 8,000 today. In 10 years there will probably be no deep mines left in the UK.
It is true that some of the mines were not economical, but the government wanted to get rid of the NUM, and if that meant all the pits as well, then so be it. The economic argument didn't add up because there is a much bigger picture than just whether a pit is profitable. There is a huge extended cost when the major source of employment, eg the the pit, is gone e.g. social security benefits, crime, drugs, etc. etc. In other (more enlightened/less vindictive) coal producing countries, e.g. Germany, the uneconomic pits were subsidised to stay open because this was the cheapest and best option - and self- suffiency in coal was retained. In this country we now rely on imports and a privatised industry which obviously puts profit above all else.
4) Different mining communities were affected in different ways. A pit closure was always a blow, but up until the 1970s, there was usually another pit with jobs to offer close by. The bigger communities were usually a little better off because there was sometimes diversity in employment, and hopefully somewhere else to go if the pit shut. However, some communities, both small and large, were almost totally reliant on coal and coal related employment. This has led to real problems of unemployment, poverty, crime and drugs in these communities, and this is the true legacy of the 1984/85 strike. Some communities are just disappearing, as the young people have to move away to find jobs. It's very sad, and very worrying - the baby was truly thrown out with the bathwater. Even if the work at the pit was dirty and dangerous, it was a job, and it bonded communities like no other job going.
Other aspects to this is that the UK is no longer self sufficient in energy - we have to import. Also the privatised coal companies make most money by opencast mining, which is basically quarrying coal from the exposed coalfield, and mostly on Green Field sites. This is very damaging environmentally, creates pollution and illness, and employs very few people for relatively short periods. Some of the former Green Fields are usually sold off to be built on. The most unfortunate aspect is that this activity is most closely associated with land around to the former coal communities - as if they haven't/aren't suffering enough. The coal companies call it reclamation/regeneration/restoration - but the reality is usually very different.