It could always be a hologram recording. Especially if he thought he might not come back from confronting Kylo.
This is actually the most interesting suggestion. Some heart felt holo recording could really offer a balance of sadness and nostalgia that doesn’t take away from his death AND it negates the need for any flashbacks. Brilliant!
“If you’re watching this, then chances are, I’m probably dead. Chewie, don’t let that crazy kid crash the Falcon too bad.”
In all seriousness, I’m not sure how I’d feel about that. It’s tidy, but Han doesn’t strike me as the kind of guy to leave a sappy note behind. He was always one to put all his cards on the table. It would work as a narrative device if done right, but at the same time would (at least to me) feel genuinely OOC.