[Me]

You should get some MF!

Yes, we have thought about it. Also Balwens, Badger Face Torwen, Talybont Welsh, Shetlands, Greyface Dartmoor, Devon & Cornwall Longwool, Teeswater, Border Leicester ......
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Well I can save you the bother with GFD - they don't milk are not hardy, have bad feet and are generally bred in small numbers completely aimlessly and proped up with large amounts of feed and creep.

The Teeswaters time could come again as a crossing ram if actually selected for something more than looks! Can't comment on the others - (though I fancy giving the Taly Welshers a go myself). I know a very nice lady who breeds Herdwicks near you MF, I keep trying to sell them on her behalf but no takers, cash only, must collect at night....

[Herdygirl]

We have bred Herdwicks for many years.  I find them a lovely breed.  They are no more flighty than any other breed of sheep and we do not have a dog, don't need one, I find that if you are a calm shepherd you will have calm sheep.  We don't have any foot problems and our land is from 300 to 800ft above sea level.  We have had few flystrike problems but you do need to keep a close eye on the lambs as strike is harder to spot on black lambs. As regards escapability, as landroverroy says if you cannot be bothered to maintain your stock fencing then anything will get out. 
Marches Farmer has it in a nutshell, if the gene pool is concentrated in one area (Cumbria) another outbreak of F and M could finish them off alltogether as there are less and less of them in that fair county.