Hi
1) never send to an address you are unsure of, insurance/tracking is expensive and if the buyer has not paid for it you could be even further out of pocket.
In the extreme case that they did not reply within a month with you sending at least weekly e-mails and dont forget they could be ill, gone on holiday just after paying (happend to me, all apologetic when they got back) you could refund their payment and relist.
I have seen one feedback instance where the person actually died !
What you do (except posting regardless) really depends on gut feeling and item value. Look at their profile have they a near perfect record for similar purchases, or a relative newbie profile number wise e.g. less than 20, or just poor rating ? All affects the judgement call.
And I repeat do not send without address confirmation, could be scam, which ever address it arrives at they could then keep the item and claim it never arrived at the other. Ok you may claim on the insurance that they not you should have paid for, and also be aware insurance does not usually cover the postage only the item value.
Like the postage the buyer pays it, you include it in your quoted p&p before they pay.
2) The buyer is very unlikely to say sorry here's some money I do not have to pay you and don't forget PayPal will take a cut from it as they did for the purchase.
You can mutually agree not to complete, but it costs you, what you do after that is a private deal outside of ebay/payPal, if they don't pay you have no comeback.
If you both end up with negative feedback as aresult then you can both apply to have the feedback withdrawn.