I think it will be theoretically possible. I assume it will require you to merge the Scripts of both the winzone (quitting the level) and the loading process and than open the new level. To create such a fast loading like half-life and create the immersion, you would have to create a impossible amount of small levels, because of FPSC's loading time while loading larger levels on a moderate PC/Mac.
Which would preforming the above nearly impossible.
(Atleast that is what I think, Don't have much experience with FPSC)
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