If something goes badly awry and you can't find a fast enough method of killing yourself, the game provides two mechanisms by which you may instantly end your current cycle.
On Giant's Deep you can locate your fellow traveler Gabbro. During your first conversation with Gabbro, they will talk about the time loop if you have already died at least once; if this is still your first flight from Timber Hearth and you haven't died yet, they'll instead talk about the experience of pairing with the statue over on Statue Island. You will need to return to Gabbro on a later loop, which will give you the option to ask about remaining calm in the face of certain death. Gabbro will offer to teach you meditation. (Note that accepting this offer will end your current loop, so if you have other stuff to do on Giant's Deep, you may want to come back close to the end of the cycle.)
If you haven't learned to meditate and you find yourself in need of a quick death, you can still quit to the title screen. The game warns you that your progress in this loop will not be saved, but so far I can find no evidence that this is actually true; every time I've done it, my log entries from the loop in which I quit were still available after I loaded the game again.