Bankruptcy isn't the only method Delta could use to reduce pilot wages. Remember, collective bargaining has an end point and provides options for both labor and a company.
No you don't enter bankruptcy just to negate labor contracts but that certainly will occur if Delta ends up in bankrtupcy. Given that pilot wages are really the only major item that DAL would reduce in bankruptcy, it is probably pretty unlikely they would enter bankrtuptcy largely with the intent of reducing pilot wages. DAL owns a higher percentage of its fleet than other carriers, including the most valuable newer aircraft so fewer leases could be renegotiated. DAL has no recent expensive terminal projects that it could walk away from. DAL's non-labor costs except pension obligations are generally in-line with the rest of the industry. And DAL is paying its current debt obligations, most of which are unsecured. If DAL wanted to dump the unsecured debt, they would not wait another year when big debt payments will have already been made. If the pilots drain the company, however, all bets are off.