'Hardiness' and burying with soil are two completely different issues. Very few plants will tolerate any significant change in soil depth over their root system. It deprives them of oxygen and will eventually kill them. If you've got excavation going on, have them excavate the forsythia at the same time, then regrade properly and replant. It should be fine.

covered forever.. probably not ... maybe.. who knows .. lol ...

the things sucker.. cant you just harvest a few suckers... and move them somewhere else??? .. and then replant on the slop in fall???

they also root in water. in a few days .. if not just being stuck in a pot of damp media ... pencil sized cuttings or a bit smaller ...

you have so many options...

ken

Thank you for the suggestions. I am a black thumb gardener. Lol Have no idea what I'm doing. I originally wanted to trim this patch back and when I got in there, literally as this patch was huge, I realized how overgrown this thing was. Many of the branches or stems were 15' long, having grown out to the sides of the patch looking for sunlight. I just hacked it off at the ground so it could start over. I left the original plants in the ground, but cut off and left a few young green ones standing there, just to mark the area. DH has since informed me this area will be covered over slightly. This work starts tomorrow. He said he scraped a smaller patch off, with the tractor one time, right down to the ground and it came back. That's why I thought it may survive being covered over. I'll go out early in the morning and see what I can do. The original plants are so thick and big, I doubt they could even be dug up for safekeeping. Thanks again for the replies.

If you dig up one small section, set it aside and keep the roots moist (not soaking wet), then replant when the grading is done, it should live.