LSP will not become obsolete, it will evolve. The entire industry is rallying around LSP, and Microsoft is constantly improving the protocol. In "ten or twenty years" LSP will have become a required feature for every programming language and every text editor. It will be essentially impossible to replace it with any other technology because of the massive investment already made in the ecosystem.

I can imagine Tree-Sitter slowly losing importance because LSP is integrating semantic highlighting, but Tree-Sitter will still be an easy option for writing grammars in the absence of a full-featured language server.