Whether the check was lost or mislaid makes no difference as the lawyer and the tenant likely signed an agreement ( a Stipulation) in court that memorialized the tender of partial rent made by the tenant and identified the check by number date and amount.
The tenant has not lost this money if the check is not cashed. If the tenant knew the check went awry the tenant would have had time to place a stop on the check. Of course, the cost should not be borne by the tenant. It is up to you and your lawyer to decide which of you will take the charge for the tenant needing to place a stop payment order on the check.
The tenant may replace the check. The court will allow for this relief but your lawyer has to deal with the issue of the check. The tenant will likely have enough time to come up with the remainder of the rent due in order to keep the apartment.
The answer provided to you is in the nature of general information. The general proposition being that you should try to avoid a bad outcome if you can.