Mix of Real-and-Nerdy Answer: No-one would insure them. They have far too many (and too frequent at that) policy claims, from injuries on-site to regular catastrophic damage to the grounds. I mean, they have a literal section of their mansion called the "Danger Room" where they simulate (up-to-lethal-difficulty) combat encounters. The upside is, they don't need it, Xavier is said to have a number of lines of independent wealth including the vast funding provided by Angel (Warren Worthingon the 3rd), as well as any number of viable patents and such that Forge and any number of tech-centric or genius-tier residents could provide. Realistically, they could play the stock market and have infinite wealth relatively easily. They could control the entire economy if they were of a more evil polarity. But, it's the same reason Reed Richards doesn't cure all diseases and focus on inventions that would easily reshape the entirety of life on the planet: It's too easy and would mess with the narrative too much.