I am gonna be a bit of a spoilsport here . While this is an interesting "what if" discussion, from the standpoint of the existing plot Radovid is the only viable contender. Henselt and Saskia (and Iorveth) can't play any major role simply because we have the choice to eliminate them in TW2
As to Natalis, his position is obviously far weaker than that of Radovid.
Having said that, as the devs have stated that TW3 will focus on Geralt's personal affairs, it probably won't be of major importance to the story. And let's not forget that there remains quite a large and thus far untapped pool of kings / rulers / leaders in the books, one of whom CD projekt story writers can choose to bring to prominence, and who are not even mentioned in ths thread because they haven't as of yet appeared in the games.
As to Natalis, his position is obviously far weaker than that of Radovid.
Having said that, as the devs have stated that TW3 will focus on Geralt's personal affairs, it probably won't be of major importance to the story. And let's not forget that there remains quite a large and thus far untapped pool of kings / rulers / leaders in the books, one of whom CD projekt story writers can choose to bring to prominence, and who are not even mentioned in ths thread because they haven't as of yet appeared in the games.