All Trump has to say is the investigation is a witch hunt and send a letter asserting his 5th Amendment right to not testify, and that he didn’t commit any crimes or violations. Just because he is ordered to submit to a deposition does not mean he has to actually answer any questions, or he can answer them in a way that doesn’t respond to the questions.
It’s a civil suit, not an “investigation”. Of course it’s a witch hunt. He has to come to the deposition, and with counsel present submit to questioning. But he can plead the fifth, etc., to his heart’s content.
I’d say let him come, and rent out Shea Stadium for the deposition and have it televised for his new Truth platform, filling the bleachers with deplorables and fake news reporters, taking care to admonish them to remain silent ‘til after the deposition, at which point he can make a regular Trump Rally out of it.
They got their deposition for the civil suit, properly fifth-amendmented and stonewalled. He makes sure to blow it up in their faces politically. They leave with their tails between their legs as the deplorables jeer and mock them, and it’s all caught on camera.