The Vikings' user agreement for TCF Bank Stadium includes language providing for use of the facility in the 2016 and 2017 seasons, if necessary, as long as the Vikes inform the U of M by October 1 , 2015 for the 2016 season and by October 1, 2016 for the 2017 season.
The Vikes pay $3,000,000 for 2014 and $3,000,000 for 2015. If their stay is extended, then they pay $3,125,000 in 2016 and $3,250,000 in 2017. Those fees consist of a "game fee" which is effectively rent and what is called the U of M's "game share" which represents funds for advertising, sponsorship, concession, and miscellaneous items. I presume this is a make good for the Vikes getting to push Pepsi when Coke has the pouring rights and US Bank when TCF has the naming rights and so forth. Expenses and facility improvements are above and beyond these fees. The user agreement spells out how soon the Vikes must pay the U of M when invoiced and has a resolution plan for disputed costs with the Vikes on the hook for interest and attorney fees in the event of such a dispute. Interest will also accrue on late payments. The rate is 6% per annum.
Plenty more to read about the agreement at the link below:
http://stmedia.startribune.com/documents/Facility+Use+Agreement+executed+by+Vikings-04.28.2013+.pdf