I am getting closer to finishing WK so I wonder what happens after I guru every kanji in level 60, or does it after I burn everything?
Nothing special happens for guruing everything. When you hit 60 you get a congrats email, a gold forum badge and access to the dead secret subforum. I’m told if you’re not already on lifetime you get an offer for a discounted lifetime sub but I already had lifetime so can’t confirm. Wanikani staff add new words or kanji to various levels a few times a year. Personally, if you’re on a lifetime sub you may as well use it to srs your leeches but if you’re paying monthly or annually I think once the number of items on your guru queue gets low it’s time to move on to input focused practice (maybe mining with anki or similar if you find stuff in your input that you want to learn).
Incidentally, you retain the gold badge and the sekrit forum access even if you let your subscription lapse. 