Slint is an open source, free software. The whole framework is on GitHub. A rug pull can't take back what's already released, and one could always fork if needed.

Btw, a rug pull can happen under even the most permissive licenses. As we've seen in the past with some project changing license or direction. That's more or less already happened with GPUI when Zed refocused development on its own needs rather than other GPUI users resulting in several forks.