Can I write off an SPV investment if it goes to zero?
Yes. If you have invested in an SPV or fund as an LP, you will receive a K-1 tax document each year that shows any taxable gains or losses from your investments. An investment that has gone to zero will be reflected in your K-1 for the year and can be written off for tax purposes.
Since VC funds pass-through tax liability to their investors (LPs), it is the responsibility of each investor to report gains / losses in their yearly taxes.