Possible, but it would be more plausible if Republic wasn't already in bankruptcy court.
But they are, so I don't think their CSeries obligations matter too much for them now. Regardless of any Delta deal, Republic can likely convince the court to null any remaining terms with Bombardier with little additional consequence, especially given CS300's missed deadlines. And all of their other contracts are being streamlined through the court process anyway.
From Delta's perspective, they just want the best deal possible.
From Bombardier's perspective, they have competing priorities. On one hand, from a
PR angle they don't want to announce losing Republic's order (40 firm + 40 options) until they absolutely have to. After all, that is a loss in the same magnitude as the Air Canada deal.
On the other hand, Republic presumably held some early delivery slots, and as mentioned Bombardier would be very keen to be able to offer them to an airline like Delta.