Nothing you do, or statistically anyone does, matters after you move on whether it's moving on from that job or moving on from this mortal coil. Regret needs to be framed in the sense of did you regret what you did at that moment for that moment.
Thinking about your accomplishments in the frame of years after your dead is going to just depress you to the point you're going to consider making that end come a whole lot sooner.
Give your grandchildren something to care about? Why would they? By the time they come around, everything you've done is old news. Then your great-grandchildren, well they won't know anything about you. Your great-great-grandchildren won't even know you existed, just like everybody else on the planet. Don't do things to try to create a legacy that no one cares about.
I regret plenty, but I also don't care that I'm a meaningless nothing in the universe.