I had the experience of accepting cancellation with the similar buyer. And then, two-three months, nothing! No orders at all. I had few orders in that period, so I was degraded to Level 0.
So I am still not sure if it is better to cancel or to have a bad rating. I still haven’t had bad rating so I cannot comment on that. But I think customer support prefers bad rating than cancellation. If you don’t accept cancellation and insist on him to accept the order (on which he will give bad rating most likely), at least, you can give him as well a bad rating and comment what happened bellow his rating on your page. You have more chances to hope that other more ethical buyer can read what you’ve written, understand, and order.
But it will be difficult if you only have one order. It is up to you to decide.
So the worst case is either you get bad rating or cancellation that impacts your order completion rate and orders stop coming. If that happens, try everything with CS, and if nothing works, I would advice you to concentrate on the other gigs, make them perfect and during the 60 days period, hope that someone will order from those gigs. You may also have access to buyer request until the 15th of the month, you can concentrate on that.
I would also consider, if you only have one rating so far and the worst case scenario happens, to close the account and start from zero with a new one. I don’t think this is against the TOS, may the more experienced sellers correct me if I am wrong.