If twitter was going to kill RSS, twitter would not provide RSS.
Sure, an online newspaper/blog/magazine can fit their headline and a shortened URL into 140 characters, but there would be no room for a blurb or image, as most newspapers include nowadays in their RSS feed.
One thing that RSS COULD learn from Twitter is to keep the summaries short, please! Some RSS feeds, in particular Smashing Magazine and Six Revisions, put the entire article into the RSS, which isn't cool especially when it's one of those bottomless "100 cool Photoshop brushes" types of articles.
Also, I've found that RSS is great for keeping up with the latest versions of open source software, for most code hosting places like SourceForge offer RSS updates when new program versions are submitted.
The idea of Twitter "killing" RSS seems completely unrealistic to me, especially since Twitter is a company and RSS is an open format... More Twitter hype.
At the end, I think that twitter will take some users away from rss, but never kill it.