I keep seeing this said online, but I disagree. So much of his net worth is illiquid market hopium based on the idea that he's a massive genius. He owns about 17% of Tesla now (and the days of him awarding himself epic bonuses are likely over, that's a shareholder group on the edge of open revolt), and that 17% share is worth about 70B, down from his TSLA holdings being worth over 200B. SpaceX is private so has no current market valuation to lean on, but I would bet that the "it's worth 140B" valuation has died a painful death along with the idea that Elon is a revolutionary genius. It's a company that does 2-2.5B in total revenue that has remained relatively flat since about 2017, even if the margins are spectacular, that's a company worth maybe 10-12B and Elon owns 47% of it. They exist mostly off of NASA contracts and Starlink revenue. Neither of which are likely to see explosive growth any time soon. The Boring Company & Neuralink are both useless from a valuation standpoint imo.
None of this is to say that he's broke, obviously. Even if everything unwinds on him and he loses "everything", he's still going to be at minimum a single digit billionaire, or wealthy beyond reason by all standards. But...it does mean that taking a personal 25B write down on twitter (which is likely when this all ends imo) is going to turn out to be a significant portion of his wealth evaporating on this move, potentially the majority of it by then.
If Tesla drops to a normalish valuation for an automaker (Elon himself said last night that Tesla is basically fucked without self driving tech playing out for them), it's maybe a 50B company. Elon's share of that is about 9B. He could sell SpaceX for ~10B and his share would be ~5B. Boring and Neuralink are worthless. Yeah...writing down 25B on burning twitter to the ground would hardly be a drop in the bucket at that point.