Cash prices will deactivate when any of the following take place:
Cash price creator manually deactivates it. Refer Manually deactivating an existing cash price for further information.
Cash price quantity limit is reached.
Midnight on cash price End Date is reached. Refer Scheduling a cash price for further information.
Therefore, if you do not specify an End Date and/or a quantity limit, it is important you manually deactivate your cash prices.