I am not a lawyer but AFAIK source code which has been released under an open source licence cannot be withdrawn afterwards. They could stop providing patches but the cannot change anything about the already released source code.
You have not mentioned which version of jBPM you are talking about. There is indeed support for jBPM 3.2 but there is none for jBPM 4.3 and as announced by JBoss/Red Hat recently there won't be any support. Instead they see jBPM 4 as the way to jBPM 5. Regarding your performance questions it depends on the version you are using. For jbpm 3.2 there are some benchmark results available in Joram's blog:
http://www.jorambarrez.be/blog/2008/04/14/short-jbpm-performance-showdown/