I know that the co-op was cancelled from the game, but I was wondering if it would be possible to include something similar to what Portal did. Have two separate plots that combine somehow. I was thinking something along the lines of Decay, as it was originally designed to be co-op based.
Go ahead, remake Decay.
Decay has been ported to PC as an HL1 mod, and I believe there is a remake mod in progress for Source, but it is not affiliated with BM.
I’m afraid that mod officially died at the end of last year 
https://www.moddb.com/mods/hazard-team1
Would be nice to see someone try and make it as a BM mod though 
It says in their Moddb page that they joined with Guard Duty’s team <<<-- Tripmine Studios