If the earnest money is not deposited as agreed then the Buyer is in Default, and the Seller can probably cancel the contract, or pursue other remedies. But you do not HAVE to.
If the seller wants to keep the buyers around you could ask for the money to be deposited and get an addendum stating that the time to deposit the money was extended, etc...
What the seller (and buyer for that matter) probably do NOT want is to get into a legal battle over earnest money and hold up the sale of the home. The buyer may have other ways of getting out of the contract (such as due diligence, or financing deadlines). But they are in default if they do not perform in depositing the money.
I am not an attorney, but I would think that, if desired, the seller could cancel the contract, and market the property for other buyers. In the Utah contracts used by agents there is a section that lists available remedies in the case of a Buyer defaulting. REad that section and see what can be done.
What does your agent say? Does this buyer have agent representation as well. What are they saying?
You may need to seek legal counsel on this if the buyer doesn't perform according to the contract.