The crankset spindle had some corrosion which had built up to the point that when pulling it out of the BB it was very difficult to remove, eventually it pulled the bearings out of the bottom bracket which has never happened to me before. You can see traces of glue meaning that these are bonded in to the bb shell, if I manage to get the bearings off the spindle, do you think its possible to epoxy the bearings back into the bb, they were running perfectly well during use?
external or integrated BB?
I've pushed out bearings from external BB's like these and then pushed new ones in without needing to glue or epoxy

Likewise. Just push it back in. if it's got any movement a bit of blue thread lock (or red if you're going to replace the whole bb rather than the bearings when they fail) will do the job
Force in = force out Shirley?
It's the top hats that are difficult to get back in, always seem to break IME
External, yeah it's a bit loose, a bit of thread lock should do just fine, thanks for the tip. I've never of anyone doing this intentionally just to replace the bearing's, is there any reason why this not done, price maybe, a new BB is around £20 so if the bearings are available for much cheaper why bother?
I have done several to replace thje bearings. Much cheaper and better berings. Top hats are a pig though. They come out so easily but the bloody well grow and won't go back.
Much cheaper and/or better bearings.
Slight edit but mainly this ^