You can extend your ship by date one time, do that first, extend it to August 7th or perhaps even the 8th.

Don't do option 1, you would not win a not as described case if the buyer open one. I would consider just option 2 or 3. If you go with option 2, if the buyer does contact during the waiting period,then just send screenshots of the message and bounced back email you've sent, and politely explain the situation, and when you do displace the the order, I would include also include a note to explain what happened and cause of the delay.

If you can't even reach the guest buyer by message/email, then, I don't think they would even know you have refunded and cancelled their order via email notifications, unless they check their payment method to see that it was refunded for some reason .