4 months after spilling ice tea, the MBP works again! but....

Hello, so the story goes like this. I spilt a like 500ml of ice tea on my MBP one dreary winter morning, my computer went crazy and turned off.. I did not try to power it on that day.. When i tried to get the spillage out, it poured out the computer... the next day or two i did try to turn it on and nothing, i plugged it in quickly and nothing... i thought that if the computer was saved, i just destroyed it by trying to turn it on.... i decied to take it to the geniuss' for repair but instead of a proper apple shop they sent me to an official apple reseller because it happend around the time the iphone 5S and C came out and apple was booked in my area for the next 4 weeks!!! i took it to the shop 3 days after the incidence, and when i got the shop, explained to them what happend and embarrasingly enough, MORE ICE CAME OUT IN THE STORE... the clerk laughed and said its prolly done, i agreed and explained that my MBP is almost fully upgraded and better then most new retina versions so i dont mind payin a good amount instead of buying a new windows computer....

1 week later i was contacted by the repair guy who said the computer wont turn it, and from the looks off it the logic board is done, he took pics and sent the computer back....

now i just had a really pretty paper holder sitting on my shelves... for fun 4 months later i decided to try to turn on the computer again and voila! IT WORKED!

the computer TURNED ON! with the exact applications i had open when the spillage occured!! amazing!!!

i been trying to push it a bit, I played some Counter strike: global offensive for 30min, the computer did heated up, but not enough for the fans to turn on like i wanted... i stopped because the graphics have dropped considerably! FPS went from 60 to 10-15 on lowest settings... I did not try any other games.

I ran almost all other apps i have, they all seem fine, with a few seconds lagg sometimes... videos run seemlessly and i cannot discover anything wrong execpt that teh battery is dead, the computer will only run if it is plugged in....

I am now wondering, what residue damage might be left? is there/will the corosion eventually lead to permanent death of my MBP? how long would that take? what is leading to bad performance in graphics? could it be just the graphic card effected? if i replace the battery, that should fix the problem with the computer having to always be conncted right? anything else i can do at this point really? thanks alot!