Not currently, the entities and weapons are reliant on a lot of the gamemode's logic that is hard to separate out. For example, the gamemode modifies the timescale to get correct timing on the animations. There is also a whole separate NPC system in the gamemode that drives the monster AI. The gamemode is also responsible for bootstrapping and compiling all of the assets used.

However, the quake2 gamemode is derived from sandbox. You can load it up in any map and it should work just like the standard sandbox gamemode.

I may revisit this later if I manage to find a clear path to separating out the entities and weapons.

Alright, cool

but it would be possible to straight up remake npcs because they are not hard coded they just run shoot and say random voice lines and die