Joyent's SmartOS is built on illumos, and illumos is a fork of Solaris Express / OpenSolaris / ONNV, and a whole bunch of former Solaris kernel engineers, who were at key positions at Sun Microsystems, and are now across several successful companies, still commit fixes and features into the illumos source code. For example, illumos has OpenZFS and KVM, two major features Snoracle Solaris doesn't have and can't take back unless they open source the code again, not that anyone cares what they do.
illumos has been a thriving project for over six years, fully independent from Oracle. There has been zero code sharing, and little interaction of any kind.
Illumos will continue on their own just like they've been doing for the last few years. They'll probably have even more freedom to innovate even, since they won't have to worry about chasing Solaris 12 compatibility.
Edit: And Joyent is one of the major sponsors of Illumos, too, so their platform definitely isn't going away.