I started an iOS update, on my jailbroken iPhone 4s, via Settings and now the iPhone is stuck in recovery mode. iTunes just wants to restore, but if I do this I will lose all my data and I don't have a backup.
Updating iOS at all on your jailbroken iPhone (including OTA) will break everything. You will not be able to recover your data from the device and you should restore in iTunes. Once restored, restore from your iCloud/iTunes backup if necessary and re-jailbreak.