They're still important and it builds good will which helps them gain more loyalty from the viewers. E.g. Facebook spies on you while Twitch supports the creators I like.
You would think that, and you'd be wrong. Many streamers dislike Twitch, in the same way many YouTubers dislike YouTube for their policies. Most stick around, because they saw what happened to Ninja, and he represented the best of what could be possible; your viewers by-and-large wont follow you, your community is on Twitch, they're not your community, they're Twitch's community.
Twitch could be a lot worse, and they'll probably get a lot worse now losing their only decent competition. The general murmur around the Twitch exclusivity deals was that they 10x'd in value and quantity after Microsoft put a price on Ninja. Unless YouTube gets serious, the same level of serious that Twitch and Mixer were, Twitch has no reason to add value to these streamers. The streamers wont leave; they can't.
And we all know YouTube won't do the right thing by their content creators, because they already don't.
This is a very dark day for content creators. Mixer failed, but it at least represented literally the only threat on Twitch's radar; there was always the question of "well what if Mixer blows up" guiding biz-dev at Twitch. Unless streamers band together and unionize, Amazon is going to crush them.
If there is 10x to be made outside of Twitch I am pretty sure content creators will organize and create their own streaming platform. They know who is who, it takes some weeks to get everybody on board and then Twitch has a serious competitor. For that reason, payout won't get down.
Except that they'd have no idea how to get started and even if they did move, nobody else would follow, just like what just happened. Twitch is the Netflix of streaming. Doesn't matter who else does what, people will watch Twitch + <other_streaming_company>
