Although it sounds a little like the Norse idea of Ragnarök, shortly after Valheim's launch some players discovered a serious "world-destroyer" bug that could reset your progress - a problem that was very much not intended. Thankfully, developer Iron Gate Studio has today rolled out a patch to address that, so now the main bug you need to worry about is the Deathsquito.
As reported by players at the time, it seems the world destroyer bug was indeed connected to logging out and pressing ALT+F4 at the same time. Following the patch, this will no longer cause the end of days.
Elsewhere in the patch notes, Iron Gate explains the biggest change is the "updated socketed backend" which should help improve connection issues. Vulkan support has also been added for Windows users to help with some crashes related to GPU drivers, and can be enabled by adding "-force-vulkan" as a launch option in the Steam properties menu for Valheim.
More amusingly, it seems that some of Valheim's bosses weren't quite challenging enough, with Iron Gate explaining "u guys are killing them too fast". The patch notes say that balancing fixes have been made to a number of bosses to make them more difficult, including Bonemass, Moder and Yagluth. At least you'll have a little longer to run away from Deathsquitos - the horrible things now have a slightly longer audio range.
As for the funky harpoon physics that created a Viking space race, the patch notes mention a "harpooned player and ship bug fix", which could refer to the exploit some people were using to make their ships sail faster. Back to wind power you go.
The full patch notes list a couple more performance changes, including a tombstone bug fix (although apparently this won't entirely eliminate the disappearing tombstones bug). It's worth noting that if you're using a dedicated server to play Valheim with friends, the server will likely need to be updated and restarted to prevent a black screen following the update. Or maybe try lighting a torch.