hello,
Simon B I know we went kind of O.T but yes I've done a 28 days+ stint in a Bunker more than once, without coming outside. rationing water purification etc.. similar to what you were hypothetically discussing. I suppose in a cave system taking into consideration the loss of creature comforts, damp living conditions, ailments from such etc.. I'm sure there would be a few who would be heading to take their chances outside rather than such conditions. It ain't easy BTW ok a 24-48 hour NBC kit dug into a trench exercise scenario etc.. try it longer term
Regards
David