At this point, I think the only way Ian will end up with Jo is if TJ dies

And let me tell you, if Ian ends up with Jo SOLELY because TJ died, that'd be the ending that would trigger the whole fandom, no matter who you ship or who you stan.
I really trust Doyak's storyteller abilities and I have my own theory that takes lots of little hints she left here and there, so I think she might give us the most sour ending, but it won't be just because but perfectly crafted to reach that point.