The FOSS code still exists, so there's nothing stopping you from continuing to use Redis, or more realistically, a Redis fork that will continue being maintaine

The FOSS code still exists, so there's nothing stopping you from continuing to use Redis, or more realistically, a Redis fork that will continue being maintained. The time spent on Redis is only wasted if nobody sets up a fork or if businesses move away from Redis because it costs money now. It sucks to see an open source project become proprietary through the SPSS, but if the community is as strong as all of those social and intellectual investments make it seem, there will be no problem maintaining an open fork. I imagine the independent open source contributors won't be as willing to contribute to Redis now, so there's a chance to maintain the open source version. This approach worked for MariaDB, LibreOffice, and a bunch of other projects that went through similar controversies.