I think you can leave it alone. I would NOT want to mess with hitting a gas line!!!
We actually had some contractors we hired hit a main gas line... oh my word... a handful of fire trucks, police officers galore... all of our neighbors had to be notified that things had to be shut off during the emergency repair... and the poor guys doing the work got a HEFTY fine and lost all the profit they would’ve made on our very expensive project! No, you do NOT want to hit a gas line.
FWIW, we’ve had plenty of trees cut down on our property over the decades and a number of them have had roots rot in place and it’s not been a problem at all.

I agree, "don't play with fire!" Roots rotting away around a gas line won't affect it. When saying "if the root actually embedded the gas line", do you mean penetrated?

"When saying "if the root actually embedded the gas line", do you mean penetrated?"

What I meant was, and I have seen this happened around a water line once, where a tree root grew around it, basically completely enveloped the pipe. I think the galvanized steel water line was leaking a little at a threaded joint, then the water attracted the roots, and eventually by the time I found the leak it was impossible to fix the leak because the pipe was inside a massive pile of roots and the only practical solution was to reroute the line around it.

Okay, see what you mean. That's definitely the most likely outcome with a leaking water pipe (or sewerage pipe) but I doubt it would happen with a gas pipe. Can you get the gas company to check for gas leaks? They'd surely have the equipment to do that. If you tell them you think the growing root may have moved and cracked the pipe they'd have to check it out.

I don't think there is a current leak. I bought the house over a year ago and at the time they did a pressure leak test inside and outside the house and it's all OK.

At the time the roots are already everywhere pushing everything out of their places. I knew it's something I needed to resolve. Three months ago I cut the tree down to the stump, and began slowly to remove the roots a bit at a time. Most of the far reaching roots are at the surface, may be 4" or 5" in diameter, half buried and half exposed. Most of the work was removing the 24"X24" concrete pads that it pushed up. So far I removed 30' of these roots and getting close to within 25' of the stump. I just didn't know what I should do with this section which runs parallel with the gas line. I wanted to remove it but didn't want to disturb the gas line in anyway.

May be I will just cut it off say 6" below grade on both ends, and leave that section buried. It will save me some work and no messing with the gas line. The root will just rot over time and the soil from above will settle in?

Yes, the root will rot slowly and the soil above it MAY settle an inch or so, but as it rots it turns into compost, basically, so it won't be an enormous problem along most of the root. By the stump, though, you may have serious settling (and mushrooms!) as the root mass decomposes.

I plan to hire a stump grinding service to take out the main stump. But the problem is there are 5" to 7" thick roots near the surface as far as 50' away. I have dug up most of it because it was pushing and cracking things up.

But as I get closer and closer to the main stump it is getting very hard. The roots are getting massive and the main stump is higher then the surrounding ground.

The picture above may be hard to see, I have drawn the outlines of the roots below.

If I grind the stump down say six to eight inches I don't think it will really touch the massive root below grade. I won't be able to plant anything there for a LONG time right?

I wouldn't plant another tree, but you could plant annuals, or vegetables, or a perennial that is easily moved. Or you could just wait a couple of years.

And, if you grind the stump (to whatever height) level, you can set a potted plant on it. Perhaps with overflowing greenery. My stump in the sun has become the perfect place to set potted succulents on and around.

You can't plant a tree exactly where the other tree was, because the ground up stump and roots will not support growth for a few years until they rot. You can move off several feet into real soil.

Yes, leave the roots alone where you can't see them and especially around any gas lines.

If I grind down eight inches, the main stump may still be protruding from the ground because the tree's original root mass has raised the ground around it into a pretty big mound.

If I plant a small tree there wouldn't the new tree's roots help penetrate into the root mass and speed up the disintegration of the big root mass? What about a palm?]

Another option I guess is to build a raised bed with concrete blocks around the tree root, then fill it with soil then plant something?

I am thinking may be a raised bed with 4x4 lumber as borders for herb.

Is it ok to use pressure treated lumber as planting borders for herb? I remember reading about the chemicals used to pressure treated are bad for edible plants but then I also read that recent pressure treating uses non toxic chemicals and is now OK, kind of?

I made a cut across the root intending the leave the rest in the ground.

About 50% through the cut I met resistance, and I knew it's not wood. I changed the angle of the cut to complete the cut so I can remove the big root sticking up. I then excavated further and found the gas pipe was indeed laying right under the tree root. Good thing I stopped as soon as I felt some resistance.

@Miami Cuse, how has everything turned out since you last posted regarding the root near the gas pipe?... especially where you cut the root close to it? Any issues? I'm facing a similar issue right now except much smaller plant and roots over my gas pipe. I'm debating if I should very carefully dig out the whole trunk/roots... OR bury the trunk and let it rot away over time.

>"stump... root mass has raised the ground around it into a pretty big mound" ___ Please update about that.