Them most likely scenario is that legal technicalities would be taken cared of, by whatever means, and the SC would eventually deem it as 'satisfactory' and move on, letting QJB continue to serve as the COAS for the extended period of time. The opposition, particularly PPP, would go along with it as it believes in minimal intervention by other institutions into civilian executive's authority, cabinet workings, and parliamentary procedures. But more importantly, PPP itself had given an extension to Gen Kayani. Thus, Aitzaz Ahsan has publically asserted that it is PM's constitutional right to appoint Army Chief, PM has the prerogative to give Army Chief an extension, and that SC does not have jurisdiction in this regard. Noteworthy thing is that if SC feels satisfied it might create legal precedence for all future COAS to seek extensions.
The second scenario is of IK unconstitutionally overruling the SC somehow, which, however, is likely to create an unprecedented and dangerous constitutional and political crisis, which IK/PTI might not be able to manage or survive. The opposition which appears to be mutedly going along with the extension might not be so silent and dormant if this happens. Of course, it largely depends on the magnitude of IK's action. He can still do something extraordinary and get away with it. He just needs to trade carefully. Also, he should revamp his constitutional advisory team. Clearly, they are not doing their job well.
The third scenario is QJB honourably resigning as the COAS.
That's an apt analysis. In any case, the Government needs to withdraw the notification for extension. Bending over backwards to grant an extension (when IK himself is on record to have said he would NEVER do such a thing), goes to show that IK is indeed a puppet and the real power lies with the COAS. Today, both the army and government have lost legitimacy.