I plan to support this for as long as I'm using Lemmy, which should be a good while.
All the script really does is generate a docker-compose.yml stack that's best for your desired setup. So even if I do stop supporting the script, you're not locked into using it. You can always manage the Docker Compose stack manually and do your own updates, which is what people not using my script will have to do anyway.
Also, I don't bake Lemmy versions directly into this script, I just pull the latest Lemmy version from GitHub and deploy that. So in theory, unless the Lemmy team changes something major, this should continue working for a long time after I stop supporting it.
If you want to be prepared, I would recommend reading up on Docker Compose and getting familiar with it!
Eventually? We already had that two weeks ago!