The regionals exist because the legacies make money outsourcing that flying and the flying is needed to support the hub and spoke model the legacies largely depend upon. The demise of the regionals will not be a money maker for the legacies, it will cost them. If they could have profited by bringing regional flying in-house the legacy managements would have done so years ago.
Similarly, the legacies aren’t doing joint ventures with foreign airlines (or in Delta’s case, actually holding considerable stock in its JVs) because they don’t think they can make money by doing it. And if their management think they will make more money by letting the foreign pilots rather than their own pilots fly their pax, they’ll try to make that happen.
The allegiance of management is to the stockholders, not to their pilot groups. If they think ‘shrinking to profitability’ is their best option, they’ll do it in a heartbeat.