the answer to the question asked in the title of this posting is: the license isn't expiring. it is enforcing the terms of that license as documented. once your deployment has fewer than 3 violations within the noted 30-day period, you will once again be able to use Splunk to search your data, indefinitely.
in the meantime, i recommend you reduce the volume of your inputs so that you no longer violate the terms of the license more than twice in a given 30-day period. here is additional information from the official product documentation about the intended use cases for Splunk Free:
"Splunk Free is designed for personal, ad-hoc search and visualization of IT data. You can use Splunk Free for ongoing indexing of small volumes (<500 MB/day) of data. Additionally, you can use it for short-term bulk-loading and analysis of larger data sets--Splunk Free allows you to bulk-load much larger data sets up to 3 times within a 30 day period. This can be useful for forensic review of large data sets."
( http://docs.splunk.com/Documentation/Splunk/latest/Admin/MoreaboutSplunkFree )
note that Splunk Free is intended for personal use. if you are using Splunk Free in an enterprise environment, and require access to support under an SLA, i recommend you purchase a license.
... View more