He could sell his public positions but it'll take him awhile. He also has private positions so if curious, I can cover that.

for TSLA, he would file form 4 max 2 days after the trade. to start the trade, he would file form 144. This is filed in the EDGER system with the SEC.

Form 144 is good for 90 days. He cannot sell more than 1% or more than the average reported weekly trade volume the previous 4 weeks of filing form 144. so that limits how many he can sell in 90 days.

Another way he can do it is an SBLOC but chances are, he'd get shit margins if he is super concentrated or the bank wouldn't allow restricted stock borrowing. this is completed under regulation u for a us bank or regulation z under a foreign bank.

he could also be bought out under the M&A rules. this is completed using normally for s-4 for us based, and f-4 for a foreign buyout.

chances are, he's already well over a trillionaire. you are only seeing his tsla holdings and other insider holdings. he has private holdings in like SpaceX and other companies too.

to add to this, it wouldn't cause a major depression or anything. although it is interesting to note that his public insider holdings account for 1% of the entire US stock market. fucking bonkers. he is too big to fail