Mixed castes and non-fire caste military

So, as far as I know, the castes are pretty restrictive in their functions and there are no interbreeding.

I was thinking of what would happen in a hypothetical situation where a group of members from other castes got stranded somewhere hostile.

Maybe some kind of accident ended up isolating a colonizing crew in a distant planet, I don't know. How would the T'au act in this position?

Would water, wind and earth caste members try to learn how to fight in order to defend themselves? How would they be viewed by the rest of society?

Considering a long term stranding, would they reproduce between castes to preserve numbers and genetic variety?

If there was one ethereal among them, would he try to preserve tradition or estimulate change for his own survival? Like forcing the others to fight, or choosing who should reproduce with who in order to create more adept soldiers?

If they somehow got in contact with the rest of the Empire later, how would this etheral be received, or even those mixed-castes? Banned, killed, shamed, erased from records?