I’m pretty sure the iPhone 13 is waterproof. Nothing will happen to it. Seriously, people drop these things into the ocean and fish them out days later and they still work. If you’re worried, you can clean it off with some soapy water and then let it air-dry.

Rice

When it left the factory, it was waterproof. Just clean it off with a damp rag and go about your day.

Also, there are tons of services you can use to back up your photos automatically.

https://shortcutsgallery.com/shortcuts/water-eject-%F0%9F%92%A7/

Try this! It’s a shortcut that vibrates your phone and tries to remove the liquid.

Newer iPhones are water resistant and rated to survive spills like that (but no deep-sea diving experiences). Honestly, your phone is probably fine.

You need to make regular iTunes or iCloud backups of your phone if your pictures are that important.

Gone forever, impossible to retrieve

Anything that is extremely important to you should be backed up constantly. Redundancy is your friend. Read up on the 3-2-1 rule.

I read horror stories of stolen laptops/phones and fried hard drives and made sure it could never happen to me.

You should have a digital backup of your photos/videos in the cloud (not just syncing like iCloud, but an actual archive) and a physical backup like your computer that should also be backed up physically (like a NAS) and digitally.

The 3-2-1 rule essentially states that in order to optimally protect data, you must have three copies of the data: the original and two backup copies. These data copies should be on two different types of media (like cloud and physical) with one copy located offsite (in case of fire or theft or electrical surge that fries the data).

The more important the data, the more vigorous you need to be in protecting it.