kay wrote:

So yes,, it is possible to cut an apple tree right back to the trunk.
But it may take a few years to come back into fruiting.

Absolutely. The tree won't die - indeed it hasn't since well-
established apples are hight resilient and can survive pretty
catastrophic damage. However, unless the shoots are thinned to form a
new framework of branches, it will develop into an unproductive 'mop'
of congested twigs. Woolly aphis (American blight) love open wounds
on apples and usually the infestation starts from there and moves to
the rest of the tree as the season progresses. Get rid of the aphids
by drenching the trunk and leafy shoots with a good systemic
insecticide, Apply this two or three times at 3 week intervals and
then leave the tree until winter when all of the leaves have fallen.
Gather any leaves and burn them - you don't want any nice cosy resting
spots from which a new infestation can start in the spring.

Select the thickest and strongest shoots which can be retained to form
the new framework. All others can be cut away. You should aim for an
open-centred tree, only choosing shoots that grow outwards and away
from each other. The principle is the much the same as for producing
a new fruit tree. The ideal is an open, goblet shape with no crossing
branches. You will find that the old trunk will continue to produce a
lot of 'water sprouts' for a few years until balance has been
restored, so you will need to rub these out as they appear. Get it
more or less right and within 3 or 4 years you should be picking your
first apples. If all else fails, use it as a support for a really
nice climbing rose and a few clematis ... and you'll still get the
occasional apple.