The maximum number of Ad Board entries allowed is 80,000 only, am I right?.
What if Ad Board entries reaches to its maximum limit?
You will not be able to add new entries
What should we do in order to extend the number of Ad Board entries?
I might suggest you to use "Active till" field in order to set the expiration date for the entry. Then you may also set up in Module settings what should be done to the expired entry. If you select "Remove from database", it might resolve your problems.