The project is not dead.
- The last release was October 2012, which does not strike me as an impossibly long time for a stable Java project.
- Documentation varies project to project. 1.x and 2.x docs being mixed together implies the documentation is poor on the project, not that the project is dead.
More importantly to assess the health of a project it's best to check its issue tracking, which for MINA can be found here. There is activity as recent as November 6th (two weeks ago) from the project chairman, per this page. Also note there is development on MINA 3.0.0 documented in July 2013 (4 months ago). From reviewing this page it seems their next release will be 3.0.0, unless some urgent patch on 2.0 comes up.
This all being said I'm strongly under the impression that Netty is the more standard choice for an NIO framework - I would make sure to understand its feature set before implementing a MINA project.