Honestly, it might be better to just do a new, similar game in the same genre and theme. NOLF is pretty long in the tooth now. Hard to compete with current shooters.
The Operative: No One Lives Forever (abbreviated as NOLF) is a first-person shooter video game developed by Monolith Productions and published by Fox Interactive, released for Windows in 2000.
That's a quarter-century ago now.
It was followed by a sequel in 2002, entitled No One Lives Forever 2: A Spy in H.A.R.M.'s Way.
Almost as long.
I mean, I don't think that the actual IP from those games is necessary to make a similar game to scratch the itch.