Shifting sands for blogs

You want to build your business blog. You go out and choose one of the industry standard tools… freely available open source tools such as WordPress or Movable Type… you build the blog and it sits there for a few years, eventually becoming a rich resource full of information.
Then the guys who built the blog platform go bust or just decide to focus on something else.
What happens to your blog when that happens?
It really is happening right now – this very blog is built on Movable Type and the company behind that tool, Six Apart, has just been acquired. They say they will continue to support the platform, but if their business is moving in a new direction then how long will it be before the effort becomes too much?
Obviously you can avoid all these issues by building everything and hosting in-house, but that increases risk, complexity, and requires disaster recovery and all that stuff the cloud is supposed to fix. 
In an ideal world, it should be possible to port the data to a new platform, but historically a lot of platforms have not been keen to support easy porting because it would facilitate customers switching to better platforms. Myspace kept people on their site for a long time because they had built up a considerable amount of information on their profile and blog, but could not port any of it to a more open platform.
But what does happen when your blog platform dies? Is that it?

Wordpress blog