I'm so sorry to hear of your loss, Bertilla and offer my deepest condolences.
I have spent a lot of time thinking about how I might react to loss of a loved one, and have ruminated on what my last words to them might be (I even have them drafted out in my Notes app on my phone!). But I received some advice a long time back on the idea of last words/last moments that stuck with me ever since. Essentially it was that we have all been conditioned, almost in a romanticized movie-ish sort of way, about perfecting those final moments, those final words, those final _(insert here)__. But what matters most is how we spent our time with them throughout the course of our lives, throughout the entirety of our relationship with that person. If my loved ones die tomorrow and I won't have had a chance to say anything profound to them, I will rest easy knowing that I showed them I loved them every single day I had with them. I think whatever we would imagine saying to them in those final moments, we should try to demonstrate to them while we have them, and I'm sure you did so with your grandfather! It also reminds me of that quote: "People may forget what you said, but they will never forget how you made them feel."
I know of course nothing will take away any regrets at this moment, but I hope this somewhat helps put things in perspective :) All the best.