He would have to sell slowly to get liquidity at a stable price. Which means he would have to file some forms that says he is selling before he can finish, which means he would have to come up with a narrative that's convincing the market that the company is still worth market price.

I'd say It's not impossible but quite unlikely that he can sell it all at current market price.

Not specifically talking about Larry, but large blocks of stock are purchased all the time by a private investor. If someone likes the share price of Oracle times the number of shares owned by Ellison, they could wire Larry the money and he offloads the shares in a single transaction.

Given the right market and regulatory timing, I think an acquisition by one of the largest US techs could pass and be for a bit more than the stock price, though it would probably at least partially be in the merged stock that he would still have to unwind.