
spoiler
Short answer: He died painfully.
So during the Board of Directors meeting, the people who sided with that geezer wanted to fire Yoon. They were celebrating their early victory till it was revealed that Yoon already bought the right to use the song that is crucial to the Dream project for 10 years and he had no intention to give them the right to use it. Unable to use the song meant that the project couldn't continue and the contract with the author specifically stated that the song was irreplaceable, if the production company tried to alter any part of it will result in an automatic contract termination. So a huge loss in this project for that geezer and his party because they invested so much into it, a foreseeable bankruptcy was in sight for them.
Then it was also revealed that Yoon was the largest shareholder of the company even without the shares he sold. He fired all of those BoD members who sided with geezer Kim. After kicking everyone out, he said to him that he knew that he was using a pacemaker and asked him what would happen if somehow it happened to malfunction. Then the last scene was Kim was agonizing in pain in his last moment.

i love that the spoiler/chairman kim's downfall was because of something Yoon has put in the contract (although he does have tons of shares but like I love how detailed he is!). I was worried that he'll only win in the end because of his family with his grandpa now taking him back. Thank goodness it was by his own merit haha. Now I can enjoy their love story (and scene ( ° ʖ °) ) more bc of this!
does anyone here have spoilersss? i read this every now and then if an update comes out so i have broken knowledge/memories of this. what's ml's trump card? does he go back to his rich fam that essentially threw him away when they thought he was autistic? how does yoon's revenge go and is it satisfying (i really wanna see chairman kim fall). i love spoilers, if u have any, pls share