49.
先生『は』あの手術『の』時何『を』考えていたんですか…？
先生 is the topic of the sentence as indicated by 『は』;
あの手術の時: that time of the surgery;
考えていた: “to think” in the past progressive;
んですか=のですか
Doctor, what were you thinking at the time of the surgery?
50.
どうせ死ぬ『と』思ってたんなら…
So I knew we had something about どうせ:
Hm… How else do I explain this… another way of translating ~なら is ‘if ~’ i.e. ‘if ~ is true’. Also, どうせ comes from どう and せよ, which is the written imperative of する, and is often used for hypothetical things, like いずれにせよ (roughly ‘whichever (one) choses’, from the structure ‘~にする’, which means ‘to choose/decide on ~’). Therefore, どうせ literally translates to ‘however (one) does i.e. acts’. That might help you understand, along with parsing the sentence as I said: [どうせ死ぬ]→なら. That is, translate どうせ死ぬ first, then add the meaning of なら.
You thought In the case that he would die no matter what
☆ Is that it? Still unclear about どうせ.