The Vixen would be out because the Chinese wont support it. Not that they cannot, but they want to force us to spend only money on them. The source code is not the issue for us and we can(and have done it) on our own for the Jf for a while.
It has to do with the Chinese playing sour puss in future developments. We need their facilities for improving the fighter and testing it; and they have a stake in the program.
As they demonstrated with anger during the crash caused by us carrying out tests on some western equipment, they do not appreciate our independent decisions when it comes to joint projects.
Makes you think about CPEC