Imagine you had a bare shell of a house...
do you plumb in a combi, with gas pipes, water pipes, radiators etc...or do you make sure it is well insulated (fraction of the cost of the above) and install efficient electric radiators?
If the electricity fails, neither will work. However, if you have efficient electric radiators, the cost of keeping your house warm will be lower, over the 15 years lifetime of the gas boiler (assumed). Hot water is another thing altogether.
If you live in a rural location where woodburners are the thing, and you have a ready supply of cheap or free wood, then you are in a win situation, and the extra pollution is outweighed by the pollution caused by producing your energy from other means...and don't even think about telling me a giant wind-turbine is cheap to produce, because it isn't, and it involves smelting to get the aluminium, mining for the copper etc etc
My sister has her own small hydro plant, so electricity is free (it took only 7 years to recover the capital outlay) and she is fortunate in owning a few hundred hectares of woodland, so her woodburner is supplied from fallen timber, free of charge. It is all about looking at options, and trying to get off-grid at every opportunity. No chance for most of us in suburbia, but let's be happy for those who get energy for nothing, money for nothing...and chicks for free!