Actually, the federal government pays for 100% of the costs associated with the expansion of Medicare for 2014-2016, 95% in 2017, 94% in 2018, 93% in 2019 and 90% in 2020 and thereafter.
So it's a pretty good deal for the states, particularly in the early years. And, given the Supreme Court's ruling, it would be stupid for any state not to participate in 2014-2016 since the federal government cannot withhold funds from the state if they decline to participate thereafter.
So, yes, the federal government would pump money into Texas and no, there is no unfunded mandate.