According to this article the Saleh Loyalists+Houthis have 100,000-120,000 fighters. I guess driving out The Hadi's isn't too diffuclt at this point. (perhaps the Hadi Loyalists can flee to Suqutra to be still there as a symbolic force). After the remaining parts of South Yemen have been taken i expect them to go on the defensive and establish a defensive line somewhere, there's no need for the Houthi's to seize East Yemen.
The only thing that can change this is a Gulfstate invasion.
http://www.middleeasterner.net/blog/...-twister-yemen
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Changed the title in accordance with recent events. I'll update the OP aswell