I think there is an annoying inconsistency int TFT when it comes to the ends of fights. Some champions (mainly summoners )get extended fights so their spells can do their work but others do not. I do not feel it is fair that Zyra's plants extend the fight and give the player a chance to win/draw/ reduce the damage done and spells like Brand's ultimate do not get the same treatment. I have had many cases where I lost the fight just because the fight ended too early and the spell did no damage and I had many cases where I won/lost the fight because of Zyra's plants or Malzahar's voidlings.
I see and understand that if fights ended as soon as all champions died the summoners would be just too weak to be in the game and I think its right to extend the fights for them but I also think that should be done for all the champions.
The fight should end when there is no spell in the air and there is not any damage over time effects on any champion and no units in be the battlefield.