Sorry for all these "What if" questions but I think this scenario could likely happen and it's better to decide what will happen now rather than later where someone will likely feel cheated...
so for example...
It's like round 3 or something (round number doesnt matter...just, we're into the war a bit)... and team happens to have 186 cards left in their vault... They decide to make six 30-card decks... Terro, Demagog, Didonko, $$$man win, Puppy and Azumi lose... therefore they gain +24 cards and -60 cards (net -36) leaving them with 150 cards, exactly enough to make 5 decks...now what I want to know, is who is out the next round since only 5 members can participate? does Terro get to choose? can he choose from everyone or must he choose from either Puppy or Azumi since they lost?...
2nd question (same scenario, continued)...
so... obviously Terro decided to kick Puppy since he's one of the worst elements players ever, next round (round 4 if we stick with the previous example) however, all five earth members win netting them +30 cards...now, was Puppy eliminated from war altogether back when team only had 150 cards or does he now come back and make a deck since they have 180 cards?
I dont think any player is "kicked" out while the team is still in the war. They just dont have enough cards to have everyone playing every round. So, if they can make only 4-5 decks, they can take turns on who's playing those decks, or however they want to organize themselves. And the decision should probably be on the Master of the element.
So in your second scenario, I believe the worst elements player ever would come back and play since they have enough cards to make him a deck to lose again with.