What's your opinion on the Master's exit on Planet Of Fire?
Depends what aspect you’re referring to—do I think it would’ve been a good exit for the character? How do I think he survived? Do I think the Doctor was right to let him burn? How do I think he was going to finish that sentence?
Regarding the first question, I’m glad he came back the next season. Obviously I just like having more Master stories, but I also don’t think it would’ve been a good end for Ainley. I mean, the Master would’ve inevitably come back at some point, but I feel Ainley gets a much better send-off in Survival. I think it takes his story full circle nicely. And I’d hate to be deprived of his interactions with Six and Seven (hot take but I think Six and Ainley are much more interesting foils for each other than Five and Ainley).
As for how the Master survived, I just don’t care. They were right not to explain it. Why waste time on pointless exposition? How the Master comes back is far less important than why you chose to bring them back and what you’re going to do with them now.
Was the Doctor right not to help him? Eh, I’m not sure I’d classify it as right or wrong. I think saving him or not saving him were both morally acceptable options in that situation. I don’t think Five was being deliberately cruel—he’s clearly agonised by his decision to stand back and let the Master die—but he hasn’t had a lot of pleasant experiences with this Master and he’s seen many people including his friends and their loved ones get hurt because of him, and he realises many more will probably suffer if he saves him. He chooses what he believes is the lesser of two evils, and is haunted by it afterwards. I think it’s no coincidence that the Master is the one he imagines urging him to die in The Caves of Androzani.
And finally, what was the Master going to say before he gets cut off? I mean, the original intention was, “Won’t you show mercy to your own brother?” They made the right call in leaving it ambiguous, and I think at this point it’s safe to say they’re definitely not siblings. I don’t really have my own headcanon on what he would have said. It could easily just have been “your own kind”.
I hope that answers your question!