On 5/3/2011 DMK passed a resolution asking its ministers in central government to quit. DMK will have no alliance with Congress and will give issue-based support to UPA.
Congress-DMK alliance was doomed when Rahul Gandhi went to Tamil Nadu, addressed Congress leaders, and said one of you will be the next chief minister of Tamil Nadu. The die was cast. Bargaining for seats was a ploy by Congress to end the alliance.
It is possible that Congress will go alone and contest all seats in Tamil Nadu. Congress did not want alliance with AIADMK.
DMK has 18 MPs in Lok Sabha. SP, BSP and other parties will be willing to join UPA. The portfolios held by DMK can be given to them. But SP and BSP are rivals of Congress in UP.
In Bihar, Congress went alone and in 2009 got five seats out of 40 in Lok Sabha election and in 2010 got four seats out of 243 in Legislative Assembly election.
Congress has been out of power in Tamil Nadu since 1967. Since some years it has been in coalition with DMK or AIADMK but not part of the government. Getting back power alone seems to be the motive of Congress.