I dont think that is correct. There is no easy way to extend a Schengen visa. Article 33 of the Schengen visa code only allows an extension if you cannot leave the Schengen area (force majeure) or you can provide “proof of serious personal reasons”.In the event of no deal. Schengen will simply become like most other countries in the world, with a visa needed if staying over 90 days.
I believe France and one or two other countries can offer long term (six months to a year) residency visas to some third country nationals but the application process takes some time and requires an appointment at a French consulate and a raft of paper work I think you also have to have proof of a residential address in France.
Trust me, as a long term traveller Ive tried to find ways around this but there just isnt any.