Yes, if they have decent arguments for it. It sounds to me like Gov did exactly what Opp asked for... they chose just one of the options. A successful Opp would've argued something like only one set of advantages is even possible, but both sets of DAs are potential, so weigh ALL scenario DAs vs. only one scenario Advs. This is screwy, but puts things in the right direction--you can accept a decent argument for just weighing all impacts (both scenarios of DAs vs. both scenarios of Advs).
In a perfect world, Opp should point out in the POO that Gov nowhere foreshadowed their intention to kick out of an arg, which Opp would surely have argued against in MO. Sounds like it may have actually happened though, in which case yeah, it's legit. Opp could've seen this coming and spiked by, when laying out the DAs, saying "we're putting our capital here, so don't let Gov kick out of their advocacy later in the round just to avoid our best set of DAs" and seeing what happened with that. If Gov doesn't touch it, fine you're good. If they do, have a huge 8 point justification for the argument in the MO.
Another thing Opp can say is that Gov COULD'VE, when the double bind came out, made a POI to state "we are fully advocating X course of actions". You'd probably have to squeeze this into the POO if you forgot to make a point along these lines earlier.