For example, can I play Flight to the Sea and target another player's Wind from the Sea if that player threated out last turn?

We know that you can target your teammates' set-aside cards if they haven't been eliminated:

The rules for the Encounter keyword do not specify that each player has a separate "set aside" zone—it seems consistent with the rules as written that there is a single "set aside" zone for the player group (like the victory display).

And RR Player Elimination doesn't seem to force the cards that a specific player set aside at the start of the game to entirely leave the game either. (They do not control those cards, nor were they ever formally part of their deck.)

There's a couple of additional rulings on player elimination, such as the two in this thread:

But neither of them seems to directly address the issue either.

So overall, I'd be inclined to say you can shuffle in a set-aside card originally from a teammate who happens to now be eliminated.

Can you use Stand and Fight on an ally in an elimnated player's discard pile?

1 hour ago, RogueSeventeen said:

Can you use Stand and Fight on an ally in an elimnated player's discard pile?

No. (That's actually one of the rulings in the second thread I linked above.)