[EvoSpace]

Spoiler for Ep11-14 Previews:

１３話「冬の城」
ライダーとの激しい戦いで宝具を解放し魔力を使い果たしてしまい倒れるセイバー。
このまま魔力を回復できなければセイバーは消えてしまうと知るが何も出来ない自分に落ち込む士 郎。

Ep 13. Winter's Castle.
Saber manage to defeat Rider after an intense fight by unleasing her Noble Phantasm and exhaust all her mana in the process. Shirou, who does not know how to replenish Saber's mana, gets worried when he knew Saber would disappear if thing carries on.

Spoiler:

As Sushi-Y said, there's a translation error here! It never says Rider was defeated. It just says, after a fierce battle with Rider, Saber released her Noble Phantasm, and that causes her to collapse from exhaust of mana.

So there's still a slight chance Rider will come back... Because I'm sure they will be revealing Sakura's past and it'll be great to have Rider in there!