How about it?
Other Players are computers.

Needs a lots of AI programming. I think there are more important features than this.

a singe player mode needs more, like:
a story
more weapons(not accessible in mp because overpowered maybe)
maybe larger maps(while in mp larger maps may cause lag in sp i think they shouldn't)
better objective of the mission(like clear the building and take the intel)
more missions than catch the intel and take it to the tent
AI players don't destroy buildings(except with rifles) but just make defenses(i don't think it would be balanced for the player be the only one able to destroy buildings but...)
mmh, maybe a really indestructible(small) base where you can enter and do...(things to think about)
EDIT:anyways, only mp is fine, and i was thinking my suggestion could be applicated also on mp...(obviously excluding AI)

I was thinking just about normal single player mode like multiplayer without story or something just playing alone

Playing alone is easy, just host a local server, and join it!