So, working my way through Fallout 2 for the first time, and I seem to have hit a little bit of a snag - while clearing out the rats in the Redding mines, my first companion, Vic the trader, ceased talking to me. That is to say, I click on him to talk to him, and all I get is a speech "bubble" over his head saying "I've had it up to here!', and that's it. It won't take me into the communication screen so I can do trading or combat control with him. I've managed to continue regardless, but have now reached NCR, and because I can't ell him to stow his gun, the local law keeps shooting at me not long after I enter the city proper. Please tell there's a way to fix this without backtracking, cause at this point that's a LOT of back tracking!

IIRC this happens if he's hit (too often?) by friendly fire in combat and there's no way to make him talk to you again.
You have to kill him or let him die.

Well... you can try to edit save file with "Fallout 2 Savegame Editor":
https://sites.google.com/site/chulancheg/

Choose save, press "Edit critters" and check if or how "Vic(00000062).pro is different from default (old save or completely new one).

How exactly does this editor work?

It will make changes in your savegame file... ;-)

Make copy of your savegame files and test it.

Place somewhere file so I (we) can check if such change is possible.

Okay, first, I'm sorry this took so long, but I was...hesitant to actually download the editor before now, but I did, and I had a look, and...nothing. I could do nothing with it to fix Vic. Mostly because the only differences I could find between the two save games I have with him before and after he stopped talking with me are that his stats in the latter were higher, as they would be by that point. But, otherwise I could find nothing about his willingness to conversate with me or not, so, whole lot of nothing. But nothing ventured, etc., etc.

There is solution (third post):
http://www.nma-fallout.com/showthread.php?199749-Fallout-2-apathetic-Vic

You have Fallout Save Editor already. I hope it's the new one (top most link/url for file "F12se.zip").

So, I followed your link, followed the instructions I found there, and...it worked! He's talking to me again! Halleluah! Thank you.

Fuck that, you should have slaughtered his stubborn ass. Dude wants to throw a hissy fit cuz of some accidental friendly fire, dude deserves what he gets. Can't be pulling a stunt like that in the wasteland.

Considering how many times almost all player characters have been blasted in the back from autofire bursts, even from miniguns, I can only agree. Vic is a big crybaby. You can finish the game without him still in the land of the living.