AMD may have no choice but to stick with 7nm. As we found out earlier nVidia preemptively booked TSMC's 5nm node, https://community.amd.com/thread/252565 , so capacity may not be there, and AMD will likely prioritize RDNA2 GPUs given Navi's inefficiencies are already showing up poorly against nVidia's 10nm Turing cards, and the Zen architecture is very efficient compared to the competition, so it can afford to be delayed. Navi Refresh will still be 7nm from what I understand, just an optimized version. The I/O chip of Ryzen 3 is likely to be reduced to 7nm as well as that node's space is freed up with the move to 5nm.
This far out though, I don't think we should discount the possibility that AMD could possibly bring out a 5nm Threadripper or EPYC product, because I haven't seen anything regarding those two lines. With Zen 3 Socket AM4 CPUs possibly increasing the core counts to 24 or 32, Threadripper especially is going to need to need to be 48 or more cores, since that platform is going to need to have something more than a quad channel memory controller and a boatload of PCIe lanes to make it viable, and at those levels 5nm is going to be required to keep power consumption under control.