Flow has code for converting LiquidThreads pages to Flow, and for converting Flow pages to wikitext. These can be combined to convert LQT pages to wikitext. This can be done without installing Flow, through the API. Does it provide decent wikitext (given that LQT -> wikitext conversion wasn't a use case it was designed for)? We should find some test pages (e.g. the support page on translatewiki.net) and test.
(See also T332103: Research Spike: Test Flow -> wikitext conversion which should probably be done first.)