I personally think that in order to repay his debt Squad will either free Marco from his handcuffs or take on Sengoku when Luffy gets up to the platform.
I think this is the case because Squad has a huge debt to repay and the best way to repay it is either directly aide in freeing ace by taking on Sengoku. The second best way is to free Marco since he can take on admiral's easily, and can contribute to the ongoing effort more than most others