How long do you think my new VEPR FM-AK will last if I run it suppressed with my silencer all time time (It's the 7.62x39 model) before something breaks?

depends on if it's overgassed to start with, the biggest issue is the carrier will act like a battering ram on the rear trunnion. the trunnion could crack and fail, but most likely the trunnion will push rearward and stretch the holes in the receiver for the rivets in the process. you would think with all the suppressor users out there we could get a company to make some adjustable AK gas blocks. I'd pay good $ for an adjustable SLR type FSB/GB for my M92 and M85 sbr's.

Yep, expensive lesson learned by me on my M92. Two of my front right side rivets shifted and now aren't flush with the receiver. I really do wish someone would make an adjustable FSB/GB as well.

I wonder if a buffer would mitigate that problem. Or a stronger drive spring? A Wolf spring perhaps? Or would that problem only exist in a pistol such as the M92 or a SBR, and not a rifle? I know SBRs have more gas pressure at the muzzle, but I don't know how much. I recall someone writing about how he drilled down into his gas block, thread tapped it, and installed a set screw inside so he could shoot his SVD suppressed.

How bad are the rivets? I only have 500 rounds through my VEPR (all suppressed) but I wonder how many thousand rounds it's going to take before it becomes an issue.

I made my silencer overbore by about 4 mm. The exit end cap is 12 mm and the last few baffles are about the same (very wide compared to commercial designs. I did that deliberately to mitigate the gas situation. Judging by how dirty my AK is after shooting, I know I still have more pressure and more gas coming back into the action than I would without a silencer. The sound reduction is still good. I was surprised how well it's working since the baffle holes are so big. I think total volume is the most important factor though.

A buffer wouldn't do anything. A stronger recoil spring might help depending how over gassed your gun is. My M92 was really overgassed if it only took about 150ish rounds to mess up my rear trunnion placement and the two front rivets. I guess how much your AK can take will depend how over gassed your gun is. The set screw in the gas block works when you have a 45 degree AKM gas block.