Your contract indicates what you are supposed to do and what the seller is supposed to do. If you didn't close on time, baring a contingency agreement that protects you, they may be able to claim the earnest money.
Now, if they don't have a back up offer ready to go and you can close a day or few later, they would probably be better off just finishing up with you.
Review your contract, talk to your agent and lender, fix whatever kept you from closing and find out when you can close. One option is to release the earnest money in exchange for the time you need to close (plus a few days for safety sake). The funds are still applied to your purchase and if you are able to close, everyone wins. Talk to your agent and lender before you offer this, to make sure you can close.