It seems there's a new termination clause included within the Yahoo and Microsoft deal, according to the SEC filing on April 20, 2015. The key date that jumps out is After October 1, 2015, either party may submit termination notification with a four month notice period.

The term of the Search Agreement remains 10 years from its commencement date, February 23, 2010, subject to earlier termination as provided in the Search Agreement. Pursuant to the Amendment, on or after October 1, 2015, either Yahoo or Microsoft may terminate the Search Agreement by delivering a written notice of termination to the other party. The Search Agreement will remain in effect for four months from the date of the termination notice to provide for a transition period, however, Yahoo’s Volume Commitment will not apply in the third and fourth months of this transition period. Yahoo and Microsoft Search Deal Now Includes Early Termination Clause [sec.gov]

Microsoft and Yahoo Agree to Amend Search Partnership [webmasterworld.com]