I'm not sure how different the UMC is from other mainline denominations. Most of us aren't what you'd call radical. Liberal in this context really means that they don't think homosexuality is such an overriding issue that they're willing to interfere with congregations that want to include them. A few years ago we voted to allow congregations that wanted to accept gays to do so. Surveys suggest that this is a position that is consistent with how US Christians feel. I believe if the UMC was a US denomination it would have made the same decision as the rest of us. Likely it would have lost some conservative congregations. But it really doesn't affect those congregations all that much, particularly if they're in areas of the country where the whole region feels the same way, so not all leave.
What is different about the UMC is the African connection. The votes simply aren't there for the UMC to go the same way as the other mainline denominations. There's a hope for some kind of compromise, but every other mainline church tried that, and it didn't work. They ended up with a straight up/down vote. I don't think compromise will work with the UMC either.
I'm sympathetic with African Methodists. They're often in areas with strong Muslim presence. Even to vote to allow gays in the US branch of the church could put their lives in danger, and they might very reasonably decide that the cause of the Gospel in their area is more important than accommodating gays in the US. I think the only possible compromise would be to separate governance in the US and Africa enough that they don't have to vote on this issue. But I doubt that will happen.
So I suspect that the UMC won't go the same way as other mainline denominations. At that point you could imagine individual liberal congregations withdrawing. But the recent events in the Western Jurisdictions suggest that you may lose whole jurisdictions. It appears that a jurisdiction is the smallest part that could effectively ignore national policy (not that doing so is healthy for the Church).