The transactions on the sort - or orphaned - branch are not considered confirmed. They are considered never having happened at all and are returned to the mempool, unless they were also included on the other, de facto branch.

Any bitcoins mined in an orphan block is never considered to having existed in the first place, to be able to be considered 'lost'. All the effort and electricity spent mining an orphan block is literally wasted.

There's a risk of double spend for every merchant or recipient of a transaction who didn't wait enough time to see the transaction confirmed in a block and several successive blocks. If he or she accepts a transaction in a block A, then delivers the product sold, the another transaction with the same input but other output is included in block B, then block A get orphaned, the merchant delivered the product and didn't receive the money. He or she can contact the buyer to settle this somehow, but that's the definition of a double spend.