Rather than keep interest of Tamil Nadu in mind, DMK is revolting because they cannot maximize their own corrupt revenues. If this falls apart, the progress of Tamil Nadu is in huge jeopardy. Hopefully some other party will ascend in Tamil Nadu soon. The two right now are just too corrupt for themselves and for the country.
Added later: An agreement has been struck and it looks as if the alliance will hold. The way the telecom sector was managed the last time around was shameful. Hopefully the DMK leaders will show more respect and love for the country this time around.