Possible mild spoilers to follow:

So, is there any way for him to survive if you don't give him a gun? Like, if I take out all the enemies in the area before leaving? Or will he always hold a grudge? All I have is a heavily upgraded pistol that I'm unwilling to part with. Have a tranq and stun gun that are my mains as I'm going through a pacifist playthrough as much as I can - pistol is there for the boss fights. Will I get it back later if I give it to him? Anyone tried?

When I did this part, I had saved right before talking to him. 
 
When he said he wanted a gun to defend himself, all I had was my upgraded 10mm pistol and my upgraded combat rifle and there was no way in hell I was giving either of those to him! So I reloaded my save, went downstars, bought a revolver, and gave that to him instead. 
 
Since you mentioned spoilers, you don't get the gun back. He does make contact while you're on your way to upper Hengsha and he gives you some extra credits for helping him out.

Spoiler ( just in case )

As far as I know, he does not survive the fight even if you take the time to kill all the enemies in the area before they even get in the same room as him. At least that's what happened in my playtrought ( en e-mail in the TYM building said so...)

@DougQuaid: There's a dude selling revolvers? Awesome, will check that out. Decided to do the side mission for Malik first, but at least now I know! You can't carry two 10mm (one upgraded and one not) can you? It just converts to ammo, right? Otherwise I would have knocked out the one armed guy in the brothel/hotel and stolen that.

there's a shitty 10mm pistol lying near Van Bruggan in one of the hotel pods you can grab before you initiate the cutscene and give that to him. (oh, drop your good pistol before you pick that one up if you got it modded, then come back and get your good pistol after the scene.

@Marz said:

there's a shitty 10mm pistol lying near Van Bruggan in one of the hotel pods you can grab before you initiate the cutscene and give that to him. (oh, drop your good pistol before you pick that one up if you got it modded, then come back and get your good pistol after the scene.

Yeah, accidentally already picked that up for ammo as I'm way too thorough with searches...

Will buy the revolver from downstairs as suggested. Should do the trick!

@DougQuaid: There's a dude selling revolvers? Awesome, will check that out. Decided to do the side mission for Malik first, but at least now I know! You can't carry two 10mm (one upgraded and one not) can you? It just converts to ammo, right? Otherwise I would have knocked out the one armed guy in the brothel/hotel and stolen that.

@OsvaldoMorenosaid:

Spoiler ( just in case )

As far as I know, he does not survive the fight even if you take the time to kill all the enemies in the area before they even get in the same room as him. At least that's what happened in my playtrought ( en e-mail in the TYM building said so...)

It might depend on what weapon you give him. I let him have a SMG and knocked out every enemy on my way out. Van Bruggen lived.

I gave him a revolver and he gave me 2000 credits later.