Sadly, whenever it happened, it had the same end result, as with so many old well-established British manufacturing companies.
Ensign were prolific camera makes over the years, I have an Ensign box camera (in blue) and an Ensign Midget folding camera, which is a tiny little thing about the size of a packet of 10 (non-kingsize) cigarettes, which was apparently popular with ladies of that era as it could easily be carried in a handbag, much like a small mobile phone is these days.
As you say, it appears Ross Ensign's failure to adopt 35mm film, combined with looming competition from Japanese imports (the import restrictions on which were being lifted in the late 50s/early 60s) sealed their fate. As an old advertisement I've got from the late 1950s said: The Yashicas are coming! Then add the Canons, the Nikons, the Minoltas, Pentax, Olympus, et al and even if Ensign had gone with 35mm I doubt they'd have survived the onslaught of mass-produced electronic goods from overseas.