RAG will have a place in the LLM world, since it's a way to obtain data/facts/info for relevant queries.

Since you asked about alternatives...

(a) "World models" where LLMs structure information into code, structured data, etc. and query those models will likely be a thing. AlphaGeometry uses this[1], and people have tried to abstract this in different ways[2].

(b) Depending on how you define RAG, knowledge graphs could be a form of RAG or alternatively an alternative to them. Companies like Elemental Cognition[3] are building distinct alternatives to RAG that use such graphs and give LLMs the ability to run queries on said graphs. Another approach here is to build "fact databases" where, you structure observations about the world into standalone concepts/ideas/observations and reference those[4]. Again, similar to RAG but not quite RAG as we know it today.

[1] https://deepmind.google/discover/blog/alphageometry-an-olymp...

[2] https://arxiv.org/abs/2306.12672

[3] https://ec.ai/

[4] https://emergingtrajectories.com/