If it does not appraise for the sale price on an FHA loan, the only choice is for the seller to reduce the price to the appraisal if you want FHA financing. Hopefully your purchase agreement is written so that a condition is the property must appraise for sale value and/or the purchase is contigent on you obtaining FHA financing. If so, I would not be too worried. If the house appraises for lower than the contract price, and the seller is unwilling to reduce price, you will likely be able to get out of contract (depending on specific language of contract) and be entitled to a refund of your earnest money deposit.
You will then be free to look for another property. Even though home prices are reasonable in Las Vegas currently, those prices are not going up any time soon in Las Vegas. The number one rule of purchasing a home (or any property) is DO NOT fall in love with property until escrow is closed. If you fall in love with the property before closing, and unforeseen issues arise, you will tend to make bad decisions in order to get the property. Relax, wait for appraisal to be completed, and analyze your options at that point.