The whole game is about building and re-building - to fully enjoy it, one need not get attached to their creations. It's a philosophical state of mind that one need to cultivate when playing Valheim. Consider the fuling raid as a helpful reset button that's kinda hard to press yourself, so the game is doing you a favor, so that you can enjoy rebuilding an even better base. Plus, because it's such an emotional experience, you will remember this attack for a long time, and it will become part of your unique Valheim story. In the end, you will emerge a stronger man.