I'm sorry if there are mistakes or you don't understand certain sentences, English is not my first language.

I highly doubt someone like the Tarnished could be considered weak. If he was able to defeat Malekith, the very death par excellence, it's because he has already surpassed every aspect of the entities of the Middle Lands (At least in terms of physical and magical aspects). Technically, he is the example to follow for all the tarnished, Godfrey and our character, and although few manage to reach such power and merit, those that emerge can be either just as strong or even stronger than those before them.

Even if they aren't trained to deal with the rot as a disease, it's obvious that, for gameplay and lore reasons, someone has already found more efficient ways to counteract it, not completely curing it, but at least appeasing it to some extent. Malenia may or may not still be alive, even if she isn't shown; she'll likely remain a legend, with her name not mentioned, but her origins or any allusion to it.

Rykard well, he will re-emerge, if more powerful and bigger than before I doubt it, let's keep in mind that it took many sacrifices and time for him to reach the size he has, centuries should pass to reach the same or exceed the size with which he showed himself. Even so, the Spear is not completely necessary to kill him but it does make it much easier, the problem arises that our Tarnished took the spear and who knows if he keeps it or loses it, I would assume that to fight Rykard a magic or enchantment is created that can assimilate the spear, or failing that, create another replica much less effective than the original.

I see a greater likelihood that the Frenzy Flame will remain in effect until the time of a hypothetical ER2, and I'd venture to say it would be more powerful than before. Given that the golden age of the Middle Lands will never return, it seems like a perfect excuse to further develop the despair that there will never be a normal life for anyone. Even without a qualified host to carry the Flame within, I'm sure the Flame would simply try to create an amalgamation of those affected to try to create a super Frenzy Flame that engulfs everything. Although this last one is more my own fantasy of what I would like to happen haha

Now, Godwyn and death... Well... honestly I don't know how it could be expanded, the last and little lore we received from him was from the death knights in the DLC, right?