I know IBM has been employing a large number of people to work on Linux. I'm not as concerned about the eventual wind-down of that as I might otherwise be: Linux is the global lifeblood of enterprise computing, and there are a lot of other existing and potential sources of wealth in this world to employ Linux developers. A dispersion of this talent, with the inevitable shift in focus to things that are not strictly IBM's prerogatives, might have a real benefit for Linux.
Past that, software development has suddenly become cheaper in any case: Linux is in the optimal position to benefit greatly from the good parts of that, largely due a legacy of good leadership, so perhaps employed developer headcount doesn't have the importance it has always had.
In any case, I have every faith that Linux's future is not tightly coupled to the fate of whatever Red Hat withers into: there is too much at stake for too many well-resourced entities to permit Linux to suffer at the hands of IBM. If you need evidence for this, consider the outcome of the IBM's attempt to tighten their grip on the RHEL distribution, and the stampede to rapidly established alternatives this induced. If more of that is in Linux's future, so be it.