Take it apart as much as you can and try and dry it out asap with tissue and then placing in a warm dry area. Give it a bit if time there and it might just work on re-boot. If not, it may well have had it.
I do not think that you can fix them. If the keypad isn't responding then you will have to take it to a local mobile phone shop, or your supplier.
yes somtimes i would prolly say it would 99% of the time
no
Yes,you could just put in a bowl of rice or give it to an iPhone repair so they could fix it.
Replace defective window regulator
no
You get a new phone.
take it to a phone fixing store
Put it in the microwave on full heat for 7 minutes. This will dry the water out and levae your phone intact..... Mostly.
Electronics in general are "ruined" once they fall in water. Try the link Fix a cell phone that fell into water.
I never washed my phone but a friend of mine dropped her phone in a sink full of water. To fix it she took out the battery and then put her phone in a bowl of dry white rice overnight. The rice absorbed all of the water from her phone and it turned on. Its worth a try.
Let the water drain out of it. Then let it dry out for 3 or 4 days and hope it works. It all depends on how much water got into the phone. If you are able to open it up it will speed up the drying time.