The parent poster's point was that it was not reasonable to consider moving off any platform that did not offer significant improvements. Now I realize that I did not painstakingly spell out the point I was making but it was not that React === Node, rather since upgrading part of your stack to a new version can have similar difficulties to moving to another language maybe moving to a different language isn't the big problem the parent poster implied.
There are multiple times during long running sites when you may need to do significant rewrites of things to move between vendors, to upgrade versions of libraries, frameworks or languages or similar things for incremental benefits.
The risk in upgrading React is lower than the risk in changing your server runtime. React still to this day guarantees a lot of backwards compatibility and the upgrade path has been thoroughly battle tested inside Facebook.
Moving to Deno is full of unknown unknowns. It’s very early.