Some 99%+ Isopropyl alcohol and a cuetip may be able to clean it up without opening it up, but it may be underneath the edge, at which point you may need to open it up to get it cleaned. Look around for a repair manual for your computer, or videos if you want to try opening it up. Without knowing your skills, I cannot say if you can/should do it yourself.
First, remove the power (unplug and pull the battery if possible) Likely there is still water in it, if the button is wet. You will need to dry it out. Getting some desiccant, and putting the laptop with it, and while making there is room for some airflow and letting it dry out; it may take a few days. Using some rice would work, as it is good to absorb moisture (put the laptop in something like a cotton pillow case, to keep the rice separate) Sadly, the longer the time between when it gets wet and when it is dried, it can allow oxidization and corrosion of the components and is a chance that it will not work.
When I ran dry, I needed to turn it from off to on 4-5 times (each time waiting for about 5 seconds at on), to get the fuel up to the engine. It then took a bit to crank, and then fired up. With it running out of gas, some sediments in the fuel tank may have been introduced into the fuel pump, and be lodged in the fuel line, or worse at the injector. (Although unlikely with a filter) I did find a video for the fuel pump/filter, may want to check it: https://www.youtube.com/watch?v=zW5_enbk...
The way I have seen lenses made, that front element is the first part assembled. It looks like you have a teardown of that lens from your second picture, which you would likely need to reverse to get it apart, and will have to disassemble the entire lens to reach it. If you open up the lens, you will be introducing even more dust as they are made in clean rooms. Be aware, that after assembly, lenses need to be calibrated, which often requires specialized equipment to get it to have the autofocus work correctly. I ignore the dust in my lenses as it doesn’t impact the ability to take pictures, and only when I stop down to f/22 do I even see it on one lens, and then only when on a solid colour, and only can see it when looking for it. All my other lenses, there is no dust spots I see in any photos, when my sensor is clean. If you have lots of dust spots in your photo, it may actually be dust on your sensor that is the cause. With a lens that has an extension when zooming, there is no way to have it completely...
There is no true wiring standard, as there is competing standards for nearly every way it can be: https://en.wikipedia.org/wiki/Phone_conn...) [Look for the TRRS section] most devices use Tip: Left audio, Ring 1:Right audio, Ring 2: Ground, Sleeve: Microphone Looking at the first photo you have it is a TRRRS with 3 rings, for a total of 5 contacts. That provides (according to wikipedia) a 2nd mic or power connection.
I would recommend checking with wherever you bought the backpack, or with Patagonia directly. From their website: "We guarantee everything we make. If you are not satisfied with one of our products at the time you receive it, or if one of our products does not perform to your satisfaction, return it to the store you bought it from or to Patagonia for a repair, replacement or refund. Damage due to wear and tear will be repaired at a reasonable charge." That makes it very likely they have the parts available. I know many of the parts are available at camping stores, and sometimes even hardware stores, too.
Does it respond at all when there is no lens mounted? Since you are saying it’s totally not responding, it is less likely (assuming none of the buttons do anything and cannot get into the menu). You could try leaving the camera without the battery in it for several days (but might need weeks, not sure on the life of it), to discharge the clock/setting internal battery, then plugging in a fully charged battery. Could check to see if the mirror is moving correctly (I had it once, where the mirror stuck half way when the camera lost power, and didn’t reset correctly, but while I had Err, it still turned off and on) If possible, try another battery, as it could be the battery is defective and not letting the camera power up either. If you don’t have one, a local camera store may have one you can use there to let you see if that is the case.