Indeed, the sequel was planned but never made.
I understand however, that 'When Worlds Collide' is still supposed to be somewhere on the Hollywood remake slate, but it's been there for years and I'm not aware of any serious start date for the project.
Speilberg was meant to be involved as a producer IIRC.
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist